Create the Flavor Foundation: In a large bowl, combine the breadcrumbs and milk. Let them soak for 5 minutes to create a panade. Meanwhile, sauté the diced onion in a pan until soft (about 5 mins), then add the minced garlic and cook for 1 more minute.
Add the cooked onions, beaten eggs, 2 tbsp ketchup, Worcestershire sauce, salt, and pepper to the panade. Mix until everything is well combined.
Combine the Meat: Add the ground beef to the bowl. Using your hands, gently mix until just combined. Be careful not to overwork the meat to ensure a tender loaf.
Bake the Loaf: Preheat your oven to 375°F (190°C). Shape the mixture into a 9x5 inch loaf on a foil-lined baking sheet. Bake for 40 minutes.
Prepare and Apply Glaze: While the meatloaf bakes, whisk together the 3/4 cup ketchup, brown sugar, and apple cider vinegar in a small bowl.
After 40 minutes, remove the meatloaf and brush half of the glaze evenly over the top and sides.
Return the loaf to the oven and bake for another 15-20 minutes. Brush with the remaining glaze during the last 5 minutes of cooking. The internal temperature should reach 160°F (71°C).
Rest and Serve: Remove the meatloaf from the oven and let it rest for 10 minutes before slicing. This is crucial for keeping it juicy.