Peel the potatoes and cut into 1-inch somewhat uniform pieces.
Boil until tender, about 12 to 15 minutes, then drain.
Add to a stand mixer with the whisk attachment (or use a hand mixer) with the sour cream and butter; mix until creamy. Since potato size varies, add more sour cream or butter until it reaches the consistency you like. I don't like adding milk because it has no flavor, but feel free to use it to loosen if you want. Season with garlic salt and pepper to taste.
Fold in 1 cup of the shredded cheddar.
Transfer to a casserole dish, top with the remaining 1/2 cup cheddar, and bake at 350 degrees for about 10 minutes, until the cheese is melted.
