1 preheat your oven to 350F2 Place your piece of bread in a food processor, and purse 10 times or until coarse crumbs measure 1/2 cup.3 Melt butter in a large saucepan over medium heat. Add onions and garlic; cook 1 minute. Add flour, cook 1 minute, stirring constantly. Gradually add milk, salt, and pepper, still stirring constantly with a whisk until blended. Bring to a boil and cook until thick, which is about 2 minutes. 4 Add cheeses and continue to stir until melted.5 Add your spinach and macaroni to cheese sauce, stirring until well blended. Spoon mixture into a 2 quart baking dish coated with cooking spray. Sprinkle with breadcrumbs. Bake at 350F for about 15 minutes or until bubbly.