Leftover Mashed Potato Soup

Mashed Potato Soup is the best way to use up leftover mashed potatoes! This creamy, cheesy, potato soup is quick to make thanks to the mashed potatoes, and it's ready to eat in just 30 minutes. Put those leftovers to good use and get another meal out of them. 

I always make this soup when I make my Cream Cheese Mashed Potatoes or these Instant Pot Mashed Potatoes for dinner or the Holidays. 

Mashed Potato Soup Recipe

I always have leftover mashed potatoes from Holiday dinners or gatherings which is why this potato soup recipe is perfect! Put those leftover mashed potatoes to good use and make this super creamy, thick, smooth, and cheesy potato soup with them. 

No need for leftovers to go to waste when you can make an entire meal with them. I love leftovers as much as anyone, but sometimes you just want to make something real with them instead of reheating. 

This soup is so simple to make with leftover mashed potatoes and a few other easy ingredients. Ready for dinner in just 30 minutes!

Ingredients Needed

• Butter - You can use unsalted butter or salted butter. I prefer salted butter with the kosher salt. If using unsalted butter then you may need to add some additional salt. Wait until the end and taste it to see. 
• All-Purpose Flour 
• Whole Milk - I highly recommend only using whole milk. You don't want something with a higher fat content or else the soup will be too thick, and you also don't want something lower in fat because then the soup might be too thin. 
• Vegetable or Chicken Broth - For a vegetarian option be sure and use vegetable broth. Either one can be used in this recipe with great results. I use vegetable broth when I make it, which is what the recipe has been tested with. 
• Leftover Mashed Potatoes - You will need 4 cups of mashed potatoes to make this soup. 
• Shredded Cheddar Cheese - Recipe has been created and tested with medium cheddar cheese. 
• Kosher Salt - You can use any salt, like sea salt or table salt, but use less if using another kind. Start with half the amount and go from there. 
• Black Pepper
• Shredded Cheddar Cheese, Sliced Green Onions, Bacon, Sour Cream - Garnishes that will elevate any bowl of potato soup. 

How to Make Mashed Potato Soup with Leftovers

Learn how to make this easy potato soup recipe. Be sure and read to the bottom of the post where you will find a printable recipe card, a pin it button so you can save it for later, and a detailed recipe card with all the ingredients and directions to make it at home. 

• Roux : Melt the butter in a large pot over medium-low heat. Once melted slowly sprinkle in the flour, while whisking constantly, until it forms a thick paste like texture. This should not take long at all. Like less than 30 seconds. Immediately add the whole milk and cook until it's thickened, while whisking frequently to prevent burning. 
• Mashed Potatoes : Add the vegetable broth and whisk it in. Bring to a simmer (which is a slight boil) and then stir in the mashed potatoes, 1 cup of the cheese, kosher salt, and ground pepper. Stir to combine. 
• Serve : The soup is ready when the cheese has melted and the soup is thick and warmed through. Serve with bacon, shredded cheddar cheese, sour cream, and sliced green onions. 

Leftover Mashed Potato Soup FAQ's

• How To Store Leftovers

  • Store any leftovers of this mashed potato soup in an airtight container for up to 3 days. 
  • When reheating, you may want to add some additional broth or milk to thin it out. The soup will get thicker as it sits in the fridge. 

• Can I Freeze Potato Soup?

  • If wanted, you can freeze this soup in a freezer-safe container or Ziploc bag for up to 2 months. 
  • I personally don't like freezing dairy products so I don't freeze this soup. As it thaws, the dairy tends to separate. 
  • Thaw in the fridge overnight before reheating for serving, or you can pop the frozen soup into the slow cooker and cook on LOW heat until warmed through.
  • You will want to add more broth or milk when reheating frozen leftovers. 

• Can I Make Substitutions?

  • Vegetable Broth : You can use chicken broth instead, or try using vegetable stock or chicken stock if wanted. The recipe calls for low-sodium broth and I do recommend sticking with that. But if wanted, feel free to use full salt broth if you prefer. 
  • Kosher Salt : I love using kosher salt because it enhances the flavors of the food rather than just make them taste salty. Feel free to use any salt you prefer, like sea salt or table salt, but reduce the amount if using another kind of salt in this soup. 
  • Bacon : Use turkey bacon.
  • Cheese : It's best to use cheddar cheese. I prefer medium cheddar cheese but you can also use mild or sharp cheddar cheese. 

Recipe Tips

• Roux Tips : A roux is what makes a soup really thick and creamy. Making a roux can be challenging if you've never made it. Here are some of my tips when making it for this recipe. When you add flour to melted butter, and whisk it, that is what creates a roux which is a thick paste texture. The key to making this is to whisk constantly and add the flour gradually. Once it is thick, smooth, and a whitish color immediately add the milk and stir until well combined. 
• Cheddar Cheese : I use medium cheddar cheese for this potato soup because it elevates the flavor profile of the mashed potatoes. You can also use mild cheddar cheese or sharp cheddar cheese if you prefer. I highly recommend grating cheese from a block instead of using shredded cheese from a bag. Freshly grated cheese melts much smoother and mixes in easier than the shredded stuff that's coated in a powder (which prevents the cheese from clumping inside the bag). 
• Garnishes : Potato soup is so much better when it's topped with bacon, shredded cheddar cheese, sour cream, and green onions. You can use bacon bits, cook bacon and chop it up, or use some microwave bacon that cooks up quickly. 
• Whole Milk : This is the best milk to use for this recipe. This helps thin out the soup, and at the same time, makes it thick and creamy. I don't recommend using a lower-fat milk because it will make the soup thinner. 
• Mashed Potatoes : These are the star of this soup! Make your favorite mashed potatoes and reserve the leftovers for this soup for another diner. You could use instant mashed potatoes (the dry potato flakes in a bag) but it might make the soup saltier so just watch the salt content and maybe don't add any until you taste the soup at the end. 

More Soup Recipes You'll Love

• Slow Cooker Creamy Potato Soup - Simple to make with frozen hash brown potato cubes. The cream cheese adds the perfect amount of rich creaminess to this soup. 
• Pasta Fagioli Soup - A hearty soup with beans, pasta, fresh vegetables, and ground beef. 
• Cream Cheese Chicken Soup - Chunks of chicken, carrot, and potato in a creamy cheese chicken broth base. 
• Slow Cooker Creamy Chicken & Wild Rice Soup - Creamy soup made in the slow cooker with a box of wild rice mix.
• Broccoli Cheese Soup with Velveeta Cheese - My family's favorite version of this classic soup. Velveeta cheese makes the soup so creamy, cheesy, and smooth. Loaded with chunks of fresh broccoli.