Place the potatoes into a pot {oven safe pot} of cold water. Bring to a boil and cook until fork tender. Drain and put back into the pot.
With the flame on low, add in the butter, garlic powder, buttermilk, salt and pepper. Mash until you've reached the texture you prefer. I leave mine with a little bit of chunk.
Add a layer of sliced fresh mozzarella on top of the mash and place under the broiler until golden.