Combine sausage, egg, breadcrumbs, apple and cheese in a large mixing bowl; stir well. Shape into 4 dozen (1-inch) balls.
In a large skillet over medium-high heat, cook in batches of 12 or 24, turning frequently until lightly browned, about 10 minutes. Drain if desired, then return to skillet.
GLAZE
In a small bowl, combine mustard, tomato sauce, maple syrup and vinegar. Pour over sausage balls. Cover and simmer for 30 minutes.
Transfer to chafing dish or slow cooker; serve hot with toothpicks.
Notes
Don't worry if you can't find the maple flavored sausage because there's maple syrup added to the recipe. The maple sausage will just make it that much better!