In a large bot of water, boil potatoes until they are fork tender and drain.
In a large mixing bowl, add butter, milk and sour cream. Using a hand mixer, mix until creamy. Add Parmesan cheese, garlic powder, salt, pepper and mix until well combined. Set aside.
In a medium saucepan, melt the butter over medium heat. Add flour and stir to form a roux. Add water, milk and crushed bouillon cubes. Stir constantly and bring to a boil.
Serve over the potatoes.