Preheat oven to 350°.
Combine ½ of the can of tomato sauce, ground beef, bread crumbs, eggs, ground black pepper, onion flakes, and salt. Mix well with your hands then place into a 5x9 inch loaf pan. Push the meatloaf into the pan to form a well for the sauce around all the edges.
Bake for 40 minutes
While baking, combine the remaining brown sugar, mustard, sugar, tomato sauce, and vinegar. Bring to a boil then remove from heat.
After meatloaf has cooked 40 minutes, cover with sauce and return to oven to bake for another 20 minutes.
Allow meatloaf to cool at least 5 minutes before you try to remove it from the pan (it sometimes crumbles).