Drain, and then drop your hunk of butter into the potatoes to start melting, along with the cream cheese. Add about 1/2 cup of milk to start, and also the sour cream. Mash well with your tool of choice. I like using my stick blender
. If it's too thick, add more milk to get the consistency you like. Stir in the salt and pepper, onions and/or garlic and bacon.