Layer sliced potatoes with onion, flour and butter, cover with milk, and bake until golden.

Steps

1. Grease a medium-sized casserole dish with butter. Slice potatoes about 1/8 inch thick.
2. Arrange potato slices in the bottom of the casserole; sprinkle with salt, black pepper, grated onion and flour; dot with butter.
3. Repeat until all potato is used. Heat enough milk to barely cover the top of the potatoes; dot top with butter.
4. Place in oven at 350°F and bake until potato is fork-tender and top is golden brown, about 45 minutes to 1 hour.
5. Remove from oven and cool 10 minutes before serving to allow sauce to thicken.