Grandma's Green Bean Casserole

2 Tablespoons butter
2 Tablespoons flour
1 teaspoon salt
1 teaspoon white sugar
1/4 cup onion, diced
1 cup sour cream
1 Tablespoon butter, melted
3 (14.5 oz.) cans French-style green beans, drained
2 cups shredded Cheddar cheese
1/2 cup buttery-round crackers.

Preheat oven to 350° degrees. Melt 2 Tablespoons butter in a large skillet over medium heat. Stir in flour until smooth and cook for 1 minute. Stir in salt, sugar, onion and sour cream. Add green beans and sir to coat. Transfer mixture to a 2-1/2 quart casserole dish. Spread shredded cheese over the top. In a small bowl, toss together the cracker crumbs and 1 Tablespoon melted butter. Sprinkle over the cheese. Bake for 30 minutes in preheated oven until top is golden and cheese is bubbly. Serves 10.