Preheat oven to 350° and spray a 3 qt baking dish with a non stick spray. Set aside.

In a large saucepan, bring 8-10 cups of water to a boil. Add potatoes and cook until tender.

Drain and set aside.

In a medium mixing bowl, stir mushroom soup, sour cream, cream cheese, butter, green onions, garlic salt and pepper together until combined.

Add 2 cups of the grated cheese and stir.

Gently stir in potatoes and mix gently until well coated.

Pour into prepared baking dish and bake for 30-35 minutes or until hot throughout.

Remove from oven and top with remaining cheese.

Once melted, top with additional green onions, optional.