Thanksgiving Scallop Potatoes, not from a box!

So I decided the make Thanksgiving day Ribs and I had those cooking on the grill and I was pondering what I would make as a side dish to my ribs when I had an 'A ha" moment, scallop potatoes.  My dad had given the Amish Friends Cookbook Volume 2 by Wanda E. Brunstetter's the night before and I was leafing through the pages checking out the recipes.  I remembered seeing the recipe for scallop potatoes.  My husband really enjoys scallop potatoes and they are somewhat of an inside joke.  When we first started dating I made my husband a special supper and I asked him what kind of potatoes he would like, he requested the really good cheesy scallop potatoes that I make.  I promptly went to start them when my mother informed me that I did not have time to cook them before the rest of my meal was done.  I have her the eye and told her that I did.  She proceeded to argue with me and I continued to give her the eye.  She then realized what I was going to make and blurted out "Oh your making the boxed scallop potatoes".  I turned a mortified shade of red.  Jokingly my husband asked me tonight if these were the boxed kind.  He almost did not get his Chocolate Pecan Pie Bars for dessert!

Home-Style Scalloped Potatoes
1/3 cup of onions, chopped
5 TBSP butter
5 TBSP flour
1 1/4 tsp salt
1/2 tsp pepper
5 cups of milk
6 cups of potatoes, thinly sliced

Preheat oven to 350 degrees.  In large saucepan, sauté onion in butter until tender.  Stir in flour, salt, and pepper.  Gradually add milk.  Bring to a boil and cook and stir 2 minutes until sauce is thickened.  Place half of potatoes in greased 3-quart baking dish.  Pour half of sauce over potatoes.  Repeat layers.  Bake uncovered 60 to 70 minutes or until potatoes are tended and top is lightly browned.