Pam spray a 9x9 pan and set aside.
Preheat the oven to 400F.
Peel and using a mandolin, slice the potatoes on the thinnest setting (1/4 inch or so).
Prepare the cheese sauce by melting the butter and adding the flour to make a roux.
Add 1/2 cup of the milk and whisk until thickened.
Add the rest of the milk and bring to a simmer, whisking frequently.
Add half the cheese and whisk until melted.
Add the rest of the cheese and the spices and whisk to blend.
Season with additional salt and pepper to taste and remove from the heat.
Place a layer of potatoes into the prepared pan and dust with salt, pepper, and the Mrs. Dash.
Add a layer of cheese.
Repeat for two more layers, gently spreading the cheese sauce to cover the top layer.
Grate a fine layer of parmesan or grana paderno cheese over the top.
Cover the pan with foil and bake for 1 hour.
Remove the foil and bake for an additional 30 minutes.