Cooking Directions:
1. Preheat oven to 350ºF.
2. Prepare pasta according to package directions; drain.
3. In a large saucepan, melt butter; stir in flour and onion. Gradually stir in milk and bring to a boil. Remove from heat.
4. Stir in cheese, salt and pepper until cheese has melted. Stir in cooked pasta.
5. Pour into a 2 1/2 quart baking dish. Bake 30 minutes.