My Favorite Macaroni and Cheese

I love this recipe for Mac n' cheese. It is very tasty and makes a great comfort food for those long winter months. Plus, the amount of butter and cheese called for is only mildly offensive.

1 lb pasta (elbow, spiral, bowtie) coked and drained
4 T butter
1 small onion, chopped
1/4 cup flour
4 cups milk
1/8 tsp cayenne pepper
1 1/4 cups (5oz) shredded cheddar cheese
1 1/4 cups shredded white cheddar or swiss cheese
8 oz diced ham
2 slices white bread
salt and pepper

1. Preheat oven to 375°. Cook pasta, and drain. In a 5-quart heavy pot, melt butter over medium heat. Add onion; cook, stirring occasionally, until softened, 3 to 5 minutes. Whisk in flour to coat onion. In a slow steady stream, whisk in milk until there are no lumps.
2. Cook, whisking often, until mixture is thick and bubbly and coats the back of a wooden spoon, 6 to 8 minutes. Stir in cayenne, if using, and 1 cup each yellow and white cheddar cheese. Season with 1 teaspoon salt and ¼ teaspoon pepper.
3. Toss pasta with cheese mixture; fold in ham. Transfer to a 9-by-13-inch baking dish. Set aside.
4. In a food processor, pulse bread until large crumbs form. Toss together with remaining ¼ cup each white and yellow cheddar, and ¼ teaspoon salt. Top pasta with breadcrumb mixture. Bake until top is golden, about 30 minutes.