First, boil potatoes until soft. This will vary in time due to many factors but you should be able to easily pierce them when they are ready.
While potatoes are boiling prep the other ingredients. Preheat oven to 350℉.
When the potatoes are don't be sure to remove any skin. With a potato masher, mash the potatoes with the butter, sour cream and cream cheese.
Once those are mixed in then fold in the parmesan and sharp cheddar cheese. Add salt and black pepper to taste.
Then transfer to a baking dish and bake for 35 minutes. The top should look a little golden but the potatoes on the top will for a crust.