Spread croutons on bottom of greased 13" x 9" baking dish. Crumble and cook sausage in medium skillet over medium heat until browned. Drain. Spread over croutons. Whisk eggs and milk in bowl until blended. Stir in soup, spinach, mushrooms, cheeses and mustard. Pour egg mixture over sausage and croutons. Refrigerate overnight. Preheat oven to 325F. Bake egg mixture 50-55 minutes or until set and lightly browned on top. Garnish with herb sprigs and carrot, if desired. Serve hot with picante sauce, if desired. Refrigerate leftovers.;