PREHEAT the oven to 400° F. Butter 13 x 9-inch baking dish.
MELT butter in large saucepan over medium heat. Add onions; cook until softened, about 2 minutes. Whisk in flour; cook, stirring constantly, until mixture turns light brown, about 3 minutes. Gradually whisk in evaporated milk, salt, black pepper, paprika and nutmeg. Reduce heat to low; cook, stirring constantly, until sauce is thickened, about 5 minutes. Add cheese and stir until melted. Add macaroni and stir until thoroughly coated. Remove from heat. Pour mixture into prepared dish. Sprinkle with bread crumbs.
BAKE for 30 to 35 minutes or until the cheese is bubbling and golden brown. Garnish with parsley, as desired.