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A white bowl with soup inside of it topped with cheese, bacon, and sour cream.

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. 
Course Soup
Cuisine American
Keyword leftover mashed potato soup, mashed potato soup, potato soup with mashed potatoes
Prep Time 10 minutes
Cook Time 20 minutes
Total Time 30 minutes
Servings 8
Calories 271kcal
Author Jessica - Together as Family


  • 4 tablespoons butter
  • ¼ cup all-purpose flour
  • 2 cups whole milk
  • 4 cups vegetable broth
  • 4 cups leftover mashed potatoes
  • 1 cup shredded medium cheddar cheese
  • ½ teaspoon kosher salt (or more to taste)
  • ½ teaspoon black pepper (or more to taste)

Garnishes for Serving

  • sour cream, shredded cheddar cheese, bacon, sliced green onion


  • In a large pot, over medium-low heat, melt the butter. Once melted slowly sprinkle in the flour, while whisking constantly, until it forms a thick paste texture.
    * This should take less than 30 seconds of constant whisking. You don't want to burn it. Just mix until it's combined and turns into a thick paste.
    * Have the flour measured out and ready to go before starting the recipe. Same thing with the milk, have it measured and ready to pour.
  • Add the whole milk and whisk together to combine. Let it simmer for about 5 minutes, while whisking frequently, until it has thickened.
  • Add the vegetable broth and bring the pot of soup to a simmer (low boil on the edges of the pot).
    * If needed, turn the heat up to medium to bring the soup with the broth to a simmer (a slight boil). Watch carefully and whisk it frequently to avoid the milk from burning.
  • Add the mashed potatoes, shredded cheddar cheese, kosher salt, and black pepper. Stir to combine everything together and to melt the cheese.
  • Soup is ready to serve when it's thicker and the cheese has fully melted into the soup. Serve with chopped bacon, additional shredded cheese, sour cream, and sliced green onions.


Serving Size : This soup serves 8 people with each serving size being equal to 1 cup of soup. The nutrition information does not include any garnishes. 
Butter : I use salted butter but unsalted butter can be used as well. 
Cheese : Recipe has been created and tested with medium cheddar cheese. You can substitute with mild or sharp cheddar cheese if wanted. I highly recommend that you grate cheese from a block for this soup. It melts smoother, it's creamier, and tastes better than the bagged shredded stuff. 
Salt : Depending on how seasoned the leftover mashed potatoes were to begin with, that can change the taste of this soup. I would start with the minimum amount of salt called for (½ teaspoon) and then taste the soup at the end and add more if necessary. The brand of broth that you buy can also make the soup taste saltier or not salty enough. When I make this recipe I use salted butter, regular vegetable broth, and then ½ teaspoon of kosher salt called for in the recipe. Adjust salt as needed. If using sea salt or table salt, start with ¼ teaspoon and add from there. 
Vegetable Broth : Recipe has been tested and created with vegetable broth. Chicken broth can be used if wanted. 
Mashed Potatoes : I recommend using leftover mashed potatoes but you can use instant mashed potatoes (dry potato flakes that you add water to) in this soup instead. Instant potatoes can be salty so just taste the soup once you add them, and add salt or don't add any depending on the taste. 
Thinner Soup : Feel free to add more broth or milk for a thinner soup. Alternately, you can also use 2% milk (although I don't recommend it) for a thinner soup. 


Calories: 271kcal | Carbohydrates: 32g | Protein: 8g | Fat: 13g | Saturated Fat: 8g | Polyunsaturated Fat: 1g | Monounsaturated Fat: 3g | Trans Fat: 0.2g | Cholesterol: 36mg | Sodium: 807mg | Potassium: 439mg | Fiber: 2g | Sugar: 5g | Vitamin A: 670IU | Vitamin C: 24mg | Calcium: 186mg | Iron: 1mg