Simple Onion Smash Burgers

Making a truly great burger at home can feel like an impossible task. After all, most home cooks struggle to get that crispy, caramelized crust you find at restaurants, and the patties often end up thick and undercooked in the middle, or so thin they dry out before you can even melt the cheese.

Luckily, these onion smash burgers solve all those problems: they’re thin enough to get that perfect crispy edge, loaded with sweet caramelized onions that practically melt into the meat, and topped with a tangy sauce that brings everything together in the most satisfying way.

What Kind of Ground Beef Should I Use?

For smash burgers, you’ll want to use ground beef with a higher fat content – aim for 80/20 (that’s 80% lean meat to 20% fat). The extra fat is key here because when you smash the burger onto a hot griddle or pan, that fat renders out and creates those crispy, caramelized edges that make smash burgers so good. Leaner ground beef like 90/10 or 93/7 won’t give you the same juicy results and can end up dry and tough. You can use ground chuck, which is usually the perfect fat ratio, and it’s typically more affordable than other cuts. Just make sure your beef is cold when you start cooking – this helps it hold together better when you’re forming and smashing the patties.

Options for Substitutions

This recipe is pretty straightforward, but here are some swaps you can make if needed:

• Mayonnaise: You can use Greek yogurt for a lighter option, though it’ll give you a tangier sauce. If you go this route, maybe add a pinch of sugar to balance it out.
• Sour cream: Plain Greek yogurt or even cream cheese (softened and thinned with a splash of milk) works well here.
• Ground beef: Stick with ground beef for this one – the fat content (aim for 80/20) is what makes these burgers juicy and helps them get that crispy crust when smashed. Leaner meats or turkey won’t give you the same result.
• American cheese: While American cheese melts beautifully, you can use cheddar, Swiss, or pepper jack if that’s what you have. Just know that American gives you that classic diner-style melt.
• Brioche buns: Potato buns or regular hamburger buns work just fine. Toast them with butter either way for the best texture.
• Onions: Yellow or white onions are best here since they caramelize nicely. Red onions are a bit too sharp for this cooking method, so I’d skip those.

Watch Out for These Mistakes While Grilling

The biggest mistake with smash burgers is pressing down on the patties multiple times during cooking, which squeezes out all those flavorful juices – smash once and walk away until it’s time to flip.

Another common error is not getting your grill hot enough before you start, as a properly heated surface is what creates that crispy, caramelized crust that makes smash burgers special.

To keep your onions from burning while the meat cooks, make sure they’re sliced thin and evenly, and press them firmly into the beef ball before smashing so they cook into the patty rather than falling off.

Finally, resist the urge to flip too early – wait until you see the edges turning brown and crispy, usually around 2-3 minutes, or you’ll tear the burger and lose that perfect crust you worked so hard to create.

What to Serve With Onion Smash Burgers?

These burgers are pretty filling on their own, so I like to keep the sides simple and classic. Crispy french fries or sweet potato fries are always a good call, and they’re perfect for dipping into any extra sauce you might have. A crunchy coleslaw adds a nice fresh contrast to the rich, savory burger, or you can go with some pickle spears and potato chips if you want something easy. For a lighter option, a simple side salad with ranch dressing rounds out the meal without making you feel too stuffed.

Storage Instructions

Store: These burgers are best enjoyed fresh off the griddle, but you can store the cooked patties separately from the buns in an airtight container in the fridge for up to 3 days. Keep the sauce in a separate container so everything stays at its best quality.

Freeze: You can freeze the cooked patties for up to 2 months. Let them cool completely, then wrap each one individually in plastic wrap before placing in a freezer bag. The caramelized onions freeze right along with them, which is super convenient for a quick meal later.

Reheat: Warm the patties in a skillet over medium heat for a few minutes on each side until heated through. You can also microwave them, but the skillet method keeps them from getting rubbery. Toast fresh buns and add new cheese for the best results.

Estimated Nutrition

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

• Calories: 3500-3800
• Protein: 135-150 g
• Fat: 220-240 g
• Carbohydrates: 175-200 g

Ingredients

For the burger sauce:

• 1/2 cup mayo (I prefer Hellmann’s mayonnaise)
• 2 tbsp sour cream
• 1.5 tbsp mustard
• 1 tsp worcestershire sauce (Lea & Perrins brand provides the best depth)
• 1/2 tsp garlic powder
• 1/2 tsp pepper
• 1/4 tsp smoked paprika
• 1/2 tsp granulated sugar

For the burgers:

• 2.2 lb ground beef (80/20 ratio for maximum juiciness)
• 2 large onions (shaved into paper-thin slices with a mandoline)
• 8 slices sharp cheddar cheese
• 4 large Brioche buns (I like St Pierre for this)
• 1 tsp kosher salt
• 1/2 tsp freshly ground black pepper
• 3 tbsp Kerrygold unsalted butter

Step 1: Make the Special Sauce and Prep Mise en Place

• 1/2 cup mayo
• 2 tbsp sour cream
• 1.5 tbsp mustard
• 1 tsp worcestershire sauce
• 1/2 tsp garlic powder
• 1/2 tsp pepper
• 1/4 tsp smoked paprika
• 1/2 tsp granulated sugar
• 2.2 lb ground beef
• 2 large onions, shaved paper-thin

Whisk together the mayo, sour cream, mustard, worcestershire sauce, garlic powder, pepper, smoked paprika, and granulated sugar in a bowl until smooth and well combined.

Set aside at room temperature.

While the sauce rests, use a mandoline to shave the onions into paper-thin slices—this is crucial for the smashing technique, as thin onions will caramelize quickly and create that signature crust.

Divide the ground beef into 8 equal portions and gently form them into balls without overworking the meat; this helps maintain the beefy texture when smashed.

Step 2: Heat the Grill and Cook First Patty Sides

• 2.2 lb ground beef
• shaved onions from Step 1
• 1 tsp kosher salt

Heat your grill to medium-high heat (around 375-400°F if using a thermometer).

Place one beef ball directly on the hot grill grate, then immediately top it with a generous handful of shaved onions and a pinch of kosher salt.

Using a sturdy spatula, press down firmly on the onions and beef, smashing them together until the patty is very thin and the onions begin to adhere to the meat.

This creates the beloved crispy, caramelized crust that defines smash burgers.

Cook without moving for 2-3 minutes until deeply browned, then flip the patty carefully using your spatula.

Step 3: Cook Second Sides and Add Cheese

• remaining ground beef
• remaining shaved onions
• kosher salt
• 8 slices sharp cheddar cheese

After flipping, cook the second side for 1-2 minutes until golden brown.

I like to add the cheese while the patty is still on the grill so it melts slightly from the residual heat—it creates better adhesion when stacking.

Top with one slice of sharp cheddar and remove from the grill.

Repeat Steps 2 and 3 with the remaining 7 beef balls, working in batches as your grill space allows, until all 8 patties are cooked with cheese melted on top.

Step 4: Stack Patties and Toast Buns

• cooked patties from Step 3
• 4 large brioche buns
• 3 tbsp Kerrygold unsalted butter

Pair up the cooked patties by placing two cheese-side-in onto each other, creating 4 double-stacked burgers with the melted cheese acting as the glue.

While the patties rest, butter both sides of each brioche bun and place them cut-side down on the grill for 1-2 minutes until golden and lightly charred.

This adds a textural contrast and prevents the buns from becoming soggy.

Step 5: Assemble and Serve

• special sauce from Step 1
• stacked patties from Step 4
• toasted buns from Step 4

Spread a generous dollop of the special sauce from Step 1 on the bottom half of each toasted bun, then place one double-stacked patty on top.

Add another light smear of sauce on the top bun and set it in place.

Serve immediately while everything is still warm and the cheese is fully melted.