Baked Crab Mac and Cheese

Ingredients

• 2 cups uncooked whole wheat elbow macaroni
• 3 tablespoons chopped onion
• 2 tablespoons butter
• 3 tablespoons all-purpose flour
• 1-1/2 cups fat-free milk
• 2 cans (6 ounces each) lump crabmeat, drained
• 1 cup reduced-fat sour cream
• 1/2 cup shredded Swiss cheese
• 1/2 teaspoon salt
• 1/2 teaspoon ground mustard
• 1 cup shredded fat-free cheddar cheese, divided