Grandma's Green Bean Casserole

2 tbsp. butter
2 tbsp. flour
1 tsp. salt
1 tsp. white sugar
1/4 cup onion, diced
1 cup sour cream
6 cups green bean pieces
2 cups shredded cheddar cheese
1/2 cup crumbled buttery crackers
1 tbsp. butter melted

Preheat oven to 350 degrees. Cook beans in boiling water till slightly tender (3 minutes if frozen, 5 minutes if fresh) and drain. Melt first amount of butter in pan. Cook onions in butter. Stir in flour till smooth. Add salt, sugar and sour cream. Add beans and cheese and stir to coat. Put into 2.5 quart dish. Toss cracker crumbs and melted butter together. Sprinkle on top of bean mixture. Bake 30 minutes.