Your potatoes sound good.
I do similar potatoes, but I cook them differently because I never seem to plan ahead long enough to cook them in the oven.
Cook in a large skillet with just enough water to cover until potatoes are cooked and the water is cooked down:
4 cups thinly sliced potatoes
1 onion sliced thin
Make cream sauce:
4 tablespoons butter
4 tablespoons flour
1 cup (more if needed, but you want the sauce fairly thick)
salt, pepper and garlic powder to taste
1- 1 1/2 cup grated sharp cheddar cheese
Melt butter in small sauce pan, add flour and cook the rue for a couple of minutes (do not let it brown). Stir in all the milk and cook on low, stirring until hot -- do not boil. Add the grated cheese and stir to melt. Season to taste. Pour over the potatoes and stir until the sauce is blended with the water. Serve