Baked Mashed Potatoes

1 T. butter
4 lbs. russet potatoes
1 cup whole milk
1 stick melted butter
1 1/2 cups grated mozarella
1 cup fresh parmesan
S&P
2 T. Bread crumbs

preheat oven to 400, coat 13X9 baking dish with butter
cook potatoes in salted boiling water about 15 min. mash mix in milk and buttermix in cheeses and top with bread crumbs and pop back into the oven until golden