Creamy Au Gratin Potatoes

4 russet potatoes, sliced into 1/4 inch slices

1 onion sliced into rings

salt and pepper *not too much pepper

3 Tbsp. butter

3 Tbsp. flour

1/2 tsp. salt

2 cups milk

1 1/2 cups shredded cheddar cheese

Preheat oven to 400. Butter a 1 qt. casserole dish. Layer 1/2 of the potatoes into bottom of the preheated casserole dish. Top with the onion slices, and add the remaining potatoes. Season w/salt and pepper. In a medium saucepan, melt butter over med. heat. Mix in flour and salt and stir constantly w/whisk for 1 min. Stir in milk. Cook until mixture has thickened. Stir in cheese all at once, and continue stirring until melted, about 30-60 sec. Pour cheese over potatoes and cover dish with foil. Bake 1 1/2 hours in preheated oven.