Preheat the oven to 350°F (175°C).
Prepare the sauce: In a small bowl, mix brown sugar, ketchup, Dijon mustard, and nutmeg. Set aside.
Make the meatloaf mixture: In a large mixing bowl, combine ground meat, breadcrumbs, onion, BBQ sauce, mustard, garlic powder, chili powder, salt, pepper, and egg. Mix until well combined.
Fill the muffin tin: Spoon the meat mixture into a 12-cup muffin tin, pressing down gently to fill the cups evenly.
Bake the meatloaf muffins: Bake for 15 minutes. Remove from the oven and soak up any excess grease with a paper towel.
Add sauce: Spoon the sauce over each meatloaf muffin and return to the oven. Bake for an additional 10-15 minutes or until fully cooked (160°F internal temperature).
Serve and enjoy: Let the meatloafs cool slightly, then serve with your favorite sides.