4 russet potatoes, sliced into 1/4 slices
1 onion, sliced into rings
3 tbsp. butter
3 tbsp. all-purpose flour
1/2 tsp. salt
2 c. milk
1 1/2 c. shredded cheddar cheese
Salt and pepper to taste

Preheat oven to 400 degrees.
Butter a 1-quart casserole dish.
Layer half of the potatoes into the bottom of the casserole dish.
Top with onion slice, and add the remaining potatoes.
Season with salt and pepper to taste.
In a medium saucepan, melt butter over medium heat.
Mix in flour and salt, and stir constantly with a whisk for 1 minute.
Stir in milk and cook until mixture has thickened.
Stir in cheese all at once, and stir until melted, about 30 to 60 seconds.
Pour cheese over the potatoes, and cover the dish with aluminum foil.
Bake for 1 1/2 hours.