Preheat the oven to 375 degrees and line a baking sheet with parchment paper.
In a large bowl, combine the ground sausage, diced apple, breadcrumbs, egg, chopped onion, sage, salt, and pepper. Mix with your hands until the ingredients are evenly distributed.
Shape the mixture into a loaf about 8 inches long and place it on the prepared baking sheet.
Bake the meatloaf for 30 minutes.
While it bakes, stir together the brown sugar, ketchup, Dijon mustard, and apple cider vinegar in a small bowl until smooth.
Remove the meatloaf from the oven and spread the glaze evenly over the top and sides.
Return the meatloaf to the oven and bake for another 15 minutes, or until the internal temperature reaches 160 degrees.
Let the meatloaf rest for 5 minutes before slicing and serving.