Preheat & Prep: Preheat the oven to 375°F (190°C). Grease a 9x5-inch loaf pan or line it with parchment paper.
Mix the Ingredients: In a large bowl, combine the ground beef, diced onion, eggs, breadcrumbs, minced garlic, milk, salt, and black pepper. Mix gently until just combined.
Shape the Meatloaf: Transfer the mixture to the loaf pan and shape it into an even loaf.
Prepare the Glaze: In a small bowl, mix ketchup, brown sugar, and Dijon mustard. Spread half of the glaze over the top of the meatloaf.
Bake: Place the meatloaf in the oven and bake for 40 minutes.
Add More Glaze & Finish Baking: Remove from the oven, spread the remaining glaze on top, and bake for an additional 15-20 minutes, or until the internal temperature reaches 160°F (71°C).
Rest & Serve: Let the meatloaf rest for 10 minutes before slicing. Serve warm with your favorite side dishes.