Butter a 9 × 13-inch baking dish.

Add a third of the potatoes and sprinkle with a third (3 T.

) of the flour and a third (2 T.

) of the butter; repeat layers two more times.

Carefully pour in the milk until it covers about ¾ of the potatoes.

Bake in a preheated 425° oven for 15 minutes; reduce heat to 375° and continue baking until done, about another 45-60 minutes.

If desired, during the last 15 minutes, sprinkle on Cheddar cheese and finish baking.