2 pounds of white potatoes (peeled and sliced)
1 medium yellow or white onions (peeled and sliced)
1/4 pound of bacon, sliced into 1 inch pieces (you can also use ham)

Layer the ingredients into large/deep baking pan.

2 cups milk
1/4 cup butter
1 teaspoon pepper
1 teaspoon salt

Heat the mixture on medium until butter is melted, and then turn up heat to bring mix to boil.
While waiting for milk to boil, mix 1/4 cup water and 2 teaspoons cornstarch then slowly pour into boiling milk while whisking until the mixture is thick (almost like pudding).

Pour milk into pan with potatoes making sure it gets into the different layers.
Cover baking pan with foil and pop it into the oven, preheated to 375 degrees.

Bake for 1 hour covered, then uncover and stir well. Depending on the thickness of the sliced potatoes they may be done or need some additional time in the oven.

Even if the potatoes are done, you should give the potatoes at least 30 minutes more in the oven uncovered. If they need more time you need to adjust as needed.