Brown onion in 2 tablespoons butter; add 2 tablespoons flour. Mix well.
Add sour cream and stir until it is mixed well. Drain water off green beans; put in large bowl. Pour mixture over green beans; salt and pepper.
Stir. Pour in baking dish; add shredded cheese over top. Bake at 350 F. for 30 minutes.
Serving Size: 4