Preheat the oven with 375 F.
Spray a 9x13 baking dish with cooking spray, and set to the side.
Add ¼ cup of butter into a pan, and place it over medium heat.
Once the butter starts to sizzle, add in the flour and stir.
Let the butter and flour mixture cook for 3 minutes.
Pour in the half & half and stir.
Sprinkle in the seasoning salt and black pepper, mix.
Turn off the heat, and stir the sauce. Remove the pan from the hot burner.
Add a layer of the sliced potatoes to the bottom of the baking dish. Pour half of the sauce over the potatoes, sprinkle half of the shredded cheeses over the sauce.
Repeat the layering once more.
Cover the bake dish with a lid or foil.
Bake in the oven for 35 - 40 minutes.
Take the pan out of the oven, and let it sit for 10 minutes.
Remove the foil from the bake dish, sprinkle fresh chopped parsley on top of the scalloped potatoes.
Serve and enjoy with your other favorite holiday dishes.