Creamy Au Gratin Potatoes

Thanks allrecipes!

Creamy Au Gratin Potatoes
4 russet potatoes, peeled & sliced into 1/4 inch slices
1 onion, sliced into rings (optional--I didn't)
salt and pepper to taste
3 Tbsp. butter
3 Tbsp. flour
1/2 tsp. salt
2 C. milk
1 1/2 C. shredded cheddar cheese

Preheat oven to 400 degrees F.  Spray a 1-quart casserole dish with nonstick cooking spray.

Layer 1/2 of the potatoes into bottom of prepared casserole dish.  Top with the onion slices, and add the remaining potatoes.  Season with salt and pepper to taste.

In a medium-size saucepan, melt butter over medium heat.  Mix in the flour and salt, and stir constantly witha whisk for 1 minute.  Stir in milk.  Cook until mixture has thickened.  Stir in cheese all at once, and continue stirring until melted, about 30 to 60 seconds.  Pour cheese over potatoes, and cover the dish with aluminum foil.

Bake 1 1/2 hours in the preheated oven.