In a large pot, melt the butter over medium heat and add the flour, salt and pepper. Whisk ingredients together and cook for 1 minute.
Slowly pour the chicken broth into the pan, whisking constantly until smooth.
Then add the milk, mashed potatoes and cheddar cheese. Whisk together and cook for 5 minutes stirring constantly just until the soup reaches a simmer.
Continue cooking until desired thickness is reached.
Serve with optional toppings.
