This potato soup is a great way to use up leftover mashed potatoes and turkey. It doesn’t really get any easier than this, and it’s so hearty it can stand as a meal on its own.
Place the mashed potatoes in a large soup pot over medium heat and add the milk, heavy cream, and stock. Whisk gently to incorporate, but do not overwork. Add the turkey and season with salt, pepper, and cayenne, to taste. Bring to a light boil over medium-high heat and finish by whisking in the butter.
To serve, put Gruyère in the bottom of a bowl and add soup. Garnish with a dusting of paprika and scallions.