Potatoes Au Gratin

I've been jonesing for some Scalloped Potatoes for over a week!

Here's my roux:

One medium Onion diced finely sautéed in one stick of Butter until onion is clear. Whisk in about 1/3 cup of Flour and cook stirring constantly until slightly golden. Add 3 cups of Milk mixture slowly (1 1/2 cups Half and Half, and 1 1/1 cups Milk). Stir until thickened--you might have to add a little more Flour, but if you do, sift and whisk it in as you add it to avoid lumps.

The rest is just layering your Potatoes, Cheese (I used Munster because it's creamy) and in this version diced country Ham along with the Roux.

I blanch the potatoes in salt water first to give them a head start on cooking after I slice them, 1 minute in boiling salted water usually does the trick. Bake for 40 minutes at 300˚ and then up it 425˚ for another 10 to 12 or until the top becomes nice and golden.