Overnight Make Ahead Biscuit Breakfast Casserole

I’m always looking for ways to make mornings easier, especially on weekends when everyone wants a big breakfast but I don’t want to stand at the stove flipping eggs. The answer? A good make-ahead casserole that I can prep the night before and pop in the oven while I’m still waking up.

This biscuit breakfast casserole has become my go-to when I need to feed a crowd without the stress. It’s got everything you want in a hearty breakfast – savory sausage, melty Gruyère cheese, peppers, and eggs – all soaked into day-old biscuits that soak up the custard perfectly. The best part is doing most of the work the night before, so morning me only has to turn on the oven.

I make this for holiday mornings, overnight guests, or really any time I want a warm breakfast without the chaos. Plus, it’s a great way to use up leftover biscuits that are getting a bit stale. They actually work better than fresh ones here.

What Kind of Biscuits Should I Use?

For this breakfast casserole, stale biscuits are actually your best friend since they’ll soak up all that egg mixture without getting too soggy. You can use homemade biscuits if you have leftovers from yesterday’s dinner, or grab a tube of refrigerated biscuits from the store and bake them off. If your biscuits are fresh, just leave them out on the counter for a few hours or pop them in a low oven for about 10 minutes to dry them out a bit. Buttermilk biscuits work great here, but really any style will do the job – even those flaky layers kind from the grocery store.

Options for Substitutions

This breakfast casserole is pretty forgiving when it comes to swapping ingredients:

• Biscuits: If you don’t have stale biscuits, you can use day-old bread, croissants, or even English muffins cut into chunks. Fresh biscuits work too – just let them sit out for an hour or toast them lightly so they don’t get too soggy.
• Breakfast sausage: Feel free to use bacon, ham, or turkey sausage instead. You can also skip the meat entirely for a vegetarian version and add more veggies like mushrooms or zucchini.
• Bell peppers: Any color bell pepper works here, or you can leave them out if you’re not a fan. Diced tomatoes or jalapeños make good alternatives if you want to switch things up.
• Half and half: Whole milk works just fine, or you can use a mix of milk and heavy cream. Even 2% milk will do in a pinch, though the casserole will be slightly less rich.
• Gruyère cheese: This cheese adds great flavor, but cheddar, Swiss, or Monterey Jack are all solid substitutes. You can also use a mix of whatever cheese you have on hand.

Watch Out for These Mistakes While Baking

The biggest mistake with breakfast casseroles is using raw, uncooked sausage straight into the dish, which leaves you with greasy pools of fat and undercooked meat – always brown your sausage completely and drain the excess grease before adding it to the casserole.

Another common error is not sautéing the peppers and onions first, as raw vegetables release too much moisture during baking and can make your casserole watery instead of fluffy.

To avoid a dry, overcooked casserole, pull it from the oven when the center still has a slight jiggle (around 160°F on an instant-read thermometer), since it will continue cooking as it rests.

Finally, if you’re making this ahead and refrigerating overnight, let it sit at room temperature for 20-30 minutes before baking so it cooks evenly throughout.

What to Serve With Biscuit Breakfast Casserole?

This hearty breakfast casserole is pretty filling on its own, but I love serving it with fresh fruit on the side to balance out all those rich, savory flavors. A simple fruit salad with berries, melon, and grapes works perfectly, or you could do sliced oranges or a mix of whatever’s in season. If you want something green on the plate, a light arugula salad with a lemon vinaigrette cuts through the richness nicely. For brunch gatherings, I’ll often add some crispy bacon strips or breakfast potatoes on the side, even though the casserole already has sausage in it – people seem to love having options!

Storage Instructions

Make Ahead: This casserole is perfect for making the night before! Just assemble everything in your baking dish, cover tightly with plastic wrap or foil, and pop it in the fridge overnight. In the morning, let it sit on the counter while your oven preheats, then bake as directed—you might need to add 5-10 extra minutes since it’s cold from the fridge.

Store: Leftover breakfast casserole keeps really well in the fridge for up to 4 days. Just cover the dish with foil or transfer portions to airtight containers. It’s great for grabbing a quick breakfast throughout the week!

Freeze: You can freeze this casserole either before or after baking for up to 2 months. If freezing unbaked, wrap it really well in plastic wrap and then foil. For already-baked casserole, let it cool completely first, then cut into portions and wrap individually for easy grab-and-go breakfasts.

Reheat: Warm up individual portions in the microwave for about 1-2 minutes, or reheat the whole casserole covered with foil in a 350°F oven for 15-20 minutes until heated through. If reheating from frozen, thaw in the fridge overnight first for best results.

Estimated Nutrition

Estimated nutrition for the whole recipe (without optional ingredients):

• Calories: 2400-2700
• Protein: 110-125 g
• Fat: 160-180 g
• Carbohydrates: 120-150 g

Ingredients

For the casserole base:

• 1/2 lb ground breakfast sausage (I use Jimmy Dean)
• 1/2 onion (finely diced)
• 1/2 green bell pepper (diced into 1/4-inch pieces)
• 1.5 cups Gruyère cheese (freshly shredded for better melting)
• 1/2 red bell pepper (diced into 1/4-inch pieces)
• 6 to 8 stale biscuits (day-old works best for structure)

For the custard:

• 1/2 cup Gruyère cheese (freshly shredded)
• 1/2 tsp kosher salt
• 1/4 tsp black pepper
• 6 large eggs (room temperature)
• 1 cup half and half (or heavy cream for extra richness)

Step 1: Prepare Mise en Place and Preheat Oven

• 1/2 onion, finely diced
• 1/2 green bell pepper, diced
• 1/2 red bell pepper, diced
• 1.5 cups Gruyère cheese, freshly shredded
• 0.5 cup Gruyère cheese, freshly shredded
• 6 to 8 stale biscuits, cut into pieces

Preheat your oven to 350°F and lightly grease a 9×13-inch baking dish.

Dice the onion into small, uniform pieces and cut both the red and green bell peppers into 1/4-inch pieces—uniform sizing ensures even cooking.

Shred the Gruyère cheese fresh (you’ll need 1.5 cups plus 0.5 cup reserved for topping), as freshly shredded cheese melts more evenly than pre-shredded.

Cut the day-old biscuits into quarters or halves depending on their size; stale biscuits hold their structure better than fresh ones and won’t turn to mush in the egg custard.

Step 2: Cook the Sausage and Vegetables

• 1/2 lb ground breakfast sausage
• 1/2 onion, diced
• 1/2 green bell pepper, diced
• 1/2 red bell pepper, diced

Heat a large skillet over medium-high heat and add the ground breakfast sausage, breaking it into small crumbles as it cooks for about 4-5 minutes until browned and cooked through.

Remove the sausage to a plate and set aside.

In the same skillet (keeping the rendered fat for flavor), add the diced onion and both bell peppers, sautéing for 3-4 minutes until softened but still slightly firm—you want them to retain some texture since they’ll continue cooking in the oven.

I like to keep the heat at medium so the vegetables don’t brown too much and maintain their bright color.

Step 3: Assemble the Casserole Base

• 6 to 8 stale biscuits, cut into pieces
• cooked sausage from Step 2
• sautéed vegetables from Step 2
• 1.5 cups Gruyère cheese, freshly shredded

Scatter the cut biscuit pieces evenly across the bottom of your prepared baking dish.

Distribute the cooked sausage from Step 2 over the biscuits, then scatter the sautéed vegetables from Step 2 on top.

Sprinkle the 1.5 cups of shredded Gruyère cheese over everything, making sure it’s distributed fairly evenly.

This layering method ensures every bite has sausage, vegetables, and cheese throughout the casserole.

Step 4: Make and Pour the Egg Custard

• 6 large eggs, room temperature
• 1 cup half and half
• 1/2 tsp kosher salt
• 1/4 tsp black pepper

In a bowl, whisk together the room-temperature eggs, half and half, kosher salt, and black pepper until well combined and smooth.

I recommend using room temperature eggs because they incorporate more evenly with the cream and create a more uniform custard.

Pour this mixture slowly and evenly over the assembled casserole, ensuring the liquid reaches all areas and soaks into the biscuits.

Let the casserole sit at room temperature for at least 30 minutes (or up to 8 hours refrigerated) to allow the biscuits to absorb the custard—this resting period is crucial for a tender, cohesive casserole rather than a watery one.

Step 5: Bake and Finish

• 0.5 cup Gruyère cheese, freshly shredded

Bake the casserole at 350°F for 35-40 minutes until the egg custard is mostly set but still has a slight jiggle in the center—it will continue to cook slightly as it cools.

During the last 5 minutes of baking, sprinkle the reserved 0.5 cup of shredded Gruyère cheese evenly over the top and return to the oven to melt and lightly brown.

The casserole is done when the edges are golden, the center is set, and a knife inserted near the middle comes out clean or with just a tiny bit of custard.

Let it rest for 5 minutes before serving for easier portioning.

Overnight Make Ahead Biscuit Breakfast Casserole

Delicious Overnight Make Ahead Biscuit Breakfast Casserole recipe with step-by-step instructions.

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Prep Time 20 minutes mins

Cook Time 40 minutes mins

Total Time 1 hour hr

Servings 8 servings

Calories 2550 kcal

Ingredients

  

For the casserole base:

• 1/2 lb ground breakfast sausage (I use Jimmy Dean)
• 1/2 onion (finely diced)
• 1/2 green bell pepper (diced into 1/4-inch pieces)
• 1.5 cups Gruyère cheese (freshly shredded for better melting)
• 1/2 red bell pepper (diced into 1/4-inch pieces)
• 6 to 8 stale biscuits (day-old works best for structure)

For the custard:

• 1/2 cup Gruyère cheese (freshly shredded)
• 1/2 tsp kosher salt
• 1/4 tsp black pepper
• 6 large eggs (room temperature)
• 1 cup half and half (or heavy cream for extra richness)

Instructions

 

• Preheat your oven to 350°F and lightly grease a 9x13-inch baking dish. Dice the onion into small, uniform pieces and cut both the red and green bell peppers into 1/4-inch pieces—uniform sizing ensures even cooking. Shred the Gruyère cheese fresh (you'll need 1.5 cups plus 0.5 cup reserved for topping), as freshly shredded cheese melts more evenly than pre-shredded. Cut the day-old biscuits into quarters or halves depending on their size; stale biscuits hold their structure better than fresh ones and won't turn to mush in the egg custard.
• Heat a large skillet over medium-high heat and add the ground breakfast sausage, breaking it into small crumbles as it cooks for about 4-5 minutes until browned and cooked through. Remove the sausage to a plate and set aside. In the same skillet (keeping the rendered fat for flavor), add the diced onion and both bell peppers, sautéing for 3-4 minutes until softened but still slightly firm—you want them to retain some texture since they'll continue cooking in the oven. I like to keep the heat at medium so the vegetables don't brown too much and maintain their bright color.
• Scatter the cut biscuit pieces evenly across the bottom of your prepared baking dish. Distribute the cooked sausage from Step 2 over the biscuits, then scatter the sautéed vegetables from Step 2 on top. Sprinkle the 1.5 cups of shredded Gruyère cheese over everything, making sure it's distributed fairly evenly. This layering method ensures every bite has sausage, vegetables, and cheese throughout the casserole.
• In a bowl, whisk together the room-temperature eggs, half and half, kosher salt, and black pepper until well combined and smooth. I recommend using room temperature eggs because they incorporate more evenly with the cream and create a more uniform custard. Pour this mixture slowly and evenly over the assembled casserole, ensuring the liquid reaches all areas and soaks into the biscuits. Let the casserole sit at room temperature for at least 30 minutes (or up to 8 hours refrigerated) to allow the biscuits to absorb the custard—this resting period is crucial for a tender, cohesive casserole rather than a watery one.
• Bake the casserole at 350°F for 35-40 minutes until the egg custard is mostly set but still has a slight jiggle in the center—it will continue to cook slightly as it cools. During the last 5 minutes of baking, sprinkle the reserved 0.5 cup of shredded Gruyère cheese evenly over the top and return to the oven to melt and lightly brown. The casserole is done when the edges are golden, the center is set, and a knife inserted near the middle comes out clean or with just a tiny bit of custard. Let it rest for 5 minutes before serving for easier portioning.