Grandma's Green Bean Casserole

I made this for Thanksgiving this year with a few misgivings--how could I give up the tried and true Cream of Mushroom and French Fried Onion casserole? Boy, was I glad I did. A friend said that this was the best green bean casserole they've ever had. I got the recipe and picture from allrecipes. I'll be making this for Christmas dinner too (on the Sunday after Christmas).

2 tablespoons butter
2 tablespoons all-purpose flour
1 teaspoon salt
1 teaspoon white sugar
1/4 cup onion, diced
1 cup sour cream
3 (14.5 ounce) cans French style green beans, drained
2 cups shredded Cheddar cheese
1/2 cup crumbled buttery round crackers
1 tablespoon butter, melted


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