Green bean casserole

Ingredients

• 8 Tbsp. butter
• 1 lg. onion, chopped
• 1/4 c. flour
• 3 c. sour cream
• 2 tsp. salt
• 1 tsp. pepper
• 6 tsp. sugar
• 3 lb. frozen green beans
• 1 lb. cheddar cheese, grated
• 1 sleeve buttery round crackers, crushed