Preheat the oven to 375 degrees
Peel the potatoes, then use a mandolin, or sharp knife for a thin slice about to ¼ inches thick. Finely chop the onions.
Spray the bottoms and sides of an 8 x 8 baking dish with non-stick cooking spray. Alternate layers of potatoes, onions, flour, salt and pepper, starting with potatoes first and ending with flour mixture on top. You should have 3 layers.*See recipe notes
Top with cubed butter
Heat the milk until just before boiling.
Pour the milk over the layers in the baking dish.
Top with shredded cheese.
Bake covered until the potatoes are fork tender (approx 50 minutes).
Uncover and bake until the cheese bubbles and browns. (approx 15 minutes)
Broil for 2 minutes to get a nice golden brown top.
11.Remove the dish from the oven, and let it stand for 15 - 20 minutes or until the sauce thickens.