In a large mixing bowl, combine ground beef, bread crumbs, milk, egg, finely chopped onion, minced garlic, salt, and black pepper. Mix until just combined.

Transfer the meat mixture to a baking sheet or loaf pan, molding it into a smooth, even loaf shape about 2 inches high.

In a small mixing bowl, combine ketchup, brown sugar, and mustard, mixing well until you achieve a smooth consistency.

Spread half of the glaze evenly over the top of the shaped meatloaf.

Preheat your oven to 350°F (175°C) and bake the meatloaf for approximately 50-60 minutes until cooked through, brushing on remaining glaze during the last 10 minutes.

Remove the meatloaf from the oven and let it cool for about 10 minutes before slicing and serving.