Peel the potatoes if desired. Then, cut them into 2 inch chunks.
Add potatoes to a large pot. Fill with cold water, about an inch or two above the potatoes. Bring to a boil and let cook until the potatoes are soft and fork-tender, about 12-16 minutes.
Carefully drain the potatoes into a colander. Then, put the potatoes back into the warm pot.
Mash with a potato masher. Then mix in the remaining ingredients.
Transfer to a baking dish. Bake at 400°F for 20-25 minutes, or until the edges are browned.