Comforting Garlic Mashed Potato Soup

There’s nothing quite like a bowl of soup when the weather gets cold. I’m always looking for ways to use up leftover mashed potatoes, and turning them into soup is one of my favorites. It feels like a warm hug in a bowl, especially when you add plenty of garlic.

This garlic mashed potato soup is basically comfort food at its finest. It’s creamy, filling, and takes about 30 minutes to make. I love making a big pot on Sunday and having it ready for busy weeknights when nobody wants to cook.

The best part? You probably have most of the ingredients in your kitchen already. And if you don’t have leftover mashed potatoes, no problem. I’ll show you how to make it from scratch too.

What Kind of Mashed Potatoes Should I Use?

This soup is perfect for using up leftover mashed potatoes, and honestly, any type will work great. Whether you made them with russets, Yukon golds, or even red potatoes, they’ll all create a creamy, satisfying soup base. The key is that they should already be seasoned with garlic – if your leftovers don’t have much garlic flavor, don’t worry, you can always add some garlic powder or minced fresh garlic when you’re cooking the onions. Even if your mashed potatoes are a day or two old and have gotten a bit firm in the fridge, they’ll loosen up perfectly once you add the broth and milk.

Options for Substitutions

This cozy soup is perfect for using up leftovers, and you can easily swap ingredients based on what’s in your fridge:

• Leftover garlic mashed potatoes: This is the star of the show, so try not to substitute it! If you don’t have leftovers, make a quick batch with 2 pounds of potatoes, butter, milk, and garlic. Plain mashed potatoes work too – just add 2-3 minced garlic cloves to the soup.
• Herb butter: No herb butter? Just use regular butter and add a pinch of dried herbs like basil, parsley, or thyme as suggested. Fresh herbs work even better if you have them.
• Chicken or turkey broth: Vegetable broth works great for a lighter version, or you can use beef broth for a richer flavor. In a pinch, bouillon cubes mixed with water will do the job.
• Whole milk: Heavy cream makes it extra rich, while 2% milk keeps it lighter. For dairy-free options, try unsweetened almond milk or oat milk, though the soup won’t be quite as creamy.
• Cheddar cheese: Any melty cheese works for garnish – try Gruyere, Monterey Jack, or even cream cheese stirred right into the soup for extra richness.
• Fresh thyme: Dried thyme works fine (use about 1/2 teaspoon), or swap with rosemary, sage, or even a bay leaf while cooking.

Watch Out for These Mistakes While Cooking

The biggest mistake when making garlic mashed potato soup is adding cold milk directly to hot soup, which can cause the mixture to curdle and create an unappetizing texture – always warm your milk first or add it gradually while stirring constantly.

Another common error is not thinning the soup properly, since leftover mashed potatoes can make the soup too thick, so start with less broth and add more as needed until you reach your desired consistency.

To avoid lumpy soup, make sure to whisk vigorously when combining the mashed potatoes with the broth, or use an immersion blender for a few quick pulses to smooth everything out.

Don’t forget to taste and adjust your seasoning at the end, as leftover mashed potatoes may have lost some of their flavor and the soup might need extra salt, pepper, or garlic powder to bring it back to life.

What to Serve With Garlic Mashed Potato Soup?

This creamy soup is perfect with a warm, crusty dinner roll or some buttery biscuits for dipping and soaking up all that garlicky goodness. Since it’s such a rich and comforting soup, I like to balance it out with something fresh like a simple side salad with mixed greens and a light vinaigrette. A slice of toasted sourdough bread with a little butter works great too, especially if you want something sturdy for dunking. For a heartier meal, try serving it alongside some roasted chicken or a ham sandwich – the soup makes a perfect starter or side dish for a cozy dinner.

Storage Instructions

Refrigerate: This creamy soup keeps really well in the fridge for up to 4 days in an airtight container. Since it’s made with leftover mashed potatoes, it’s already perfect for using up what you have and then storing for easy meals throughout the week.

Freeze: You can freeze this soup for up to 3 months in freezer-safe containers or bags. Just know that dairy-based soups sometimes get a little grainy after freezing, but a good stir while reheating usually brings it back together nicely.

Warm Up: Heat it gently on the stovetop over medium-low heat, stirring frequently to prevent sticking. If it seems too thick after storing, just add a splash of milk or broth to get it back to your preferred consistency. Top with fresh cheddar cheese right before serving for the best flavor.

Preparation Time	10-15 minutes
Cooking Time	30-40 minutes
Total Time	40-55 minutes
Level of Difficulty	Easy

Estimated Nutrition

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

• Calories: 850-1000
• Protein: 25-30 g
• Fat: 35-45 g
• Carbohydrates: 110-125 g

Ingredients

For the soup:

• 3 cups leftover garlic mashed potatoes (room temperature works best)
• 1 cup whole milk (adds creaminess and richness)
• 1 stalk celery (diced into 1/4-inch pieces)
• 3 sprigs fresh thyme (for aromatic depth)
• 1 tsp canola oil
• 1 medium yellow onion (chopped into 1/4-inch pieces)
• 1 tsp herb butter (or dried basil, parsley, or thyme)
• 2 cups chicken or turkey broth (I use low-sodium)

For the topping:

• 1/4 cup shredded cheddar cheese (sharp cheddar preferred for better flavor)

Step 1: Prepare Mise en Place and Infuse Aromatics

• 1 tsp canola oil
• 1 tsp herb butter
• 3 sprigs fresh thyme
• 1 medium yellow onion
• 1 stalk celery

Chop the yellow onion and celery into 1/4-inch pieces and set aside.

Heat the canola oil and herb butter together in a large pot over medium heat.

Once the butter is melted and foaming, add the fresh thyme sprigs and let them steep for about 1 minute to infuse their aromatic oils into the fat.

This brief infusion will add subtle herbal depth to your soup without overpowering it.

Remove the thyme sprigs with a slotted spoon and discard.

Step 2: Build the Aromatic Base

• onion and celery from Step 1

Add the chopped onion and diced celery to the infused oil and butter, stirring occasionally.

Cook for about 5 minutes over medium heat until the vegetables become soft and fragrant.

This process, called sweating the aromatics, gently releases their natural flavors and creates a flavorful foundation for the soup.

You’re looking for the onions to become translucent and slightly softened, not browned.

Step 3: Combine Base Ingredients and Simmer

• 3 cups leftover garlic mashed potatoes
• 2 cups chicken or turkey broth
• 1 cup whole milk
• sautéed vegetables from Step 2

Add the leftover garlic mashed potatoes, chicken or turkey broth, and whole milk to the pot with the softened vegetables.

Stir well to combine and break up the mashed potatoes slightly—they don’t need to be completely smooth at this point since we’ll blend everything later.

Bring the mixture to a gentle simmer over medium heat, then reduce heat to medium-low.

Simmer for 15-20 minutes, stirring occasionally.

This extended gentle cooking allows the flavors to meld together beautifully.

I find that letting it simmer this long also helps the soup achieve a more cohesive, well-integrated flavor profile.

Step 4: Blend to Silky Smoothness

• simmered soup mixture from Step 3

Remove the pot from heat and let the soup cool for 2-3 minutes so it’s safe to blend.

Using an immersion blender, carefully blend the soup directly in the pot until completely smooth and silky.

If you prefer a chunkier texture, you can blend it less thoroughly, but I recommend going for a completely smooth consistency to highlight the creamy richness of the mashed potatoes.

Work in batches if using a countertop blender, being careful not to fill it more than halfway to avoid splashing hot liquid.

Step 5: Finish and Serve

• 1/4 cup shredded cheddar cheese

Taste the soup and adjust seasoning as needed with salt and pepper.

Ladle the hot soup into bowls and top each serving with a generous sprinkle of shredded sharp cheddar cheese.

The cheese will begin to melt slightly from the heat of the soup, creating pockets of rich, tangy flavor that complement the garlic and creamy potato base perfectly.