preheat oven to 400°F.

butter a 1-quart casserole dish.

layer 1/2 of the potatoes into bottom of the prepared casserole dish.

top with the onion slices and salt & pepper, and add the remaining potatoes.

season to taste.

in a medium saucepan, melt the butter over medium heat. mix in the flour and salt, and stir constantly with a whisk for one minute.

stir in the milk. cook until the mixture has thickened.

stir in the cheese all at once, and continue stirring until melted, about 30 to 60 seconds.

pour cheese over the potatoes, and cover the dish with aluminum foil.

bake 1-1/2 hours in the preheated oven.

NOTE: I added some cayenne pepper, which I always do.

RECIPE FROM: Allrecipes.com