Step 1: Preheat your oven to 350°F (175°C) and line a large rimmed baking sheet with parchment paper.
Step 2: In a small bowl, combine the breadcrumbs and milk. Stir and let sit for 5 minutes to form a panade.
Step 3: Sauté the diced onions and minced garlic in a small pan with a teaspoon of oil over medium heat until softened (about 5 minutes). Let them cool.
Step 4: In a large mixing bowl, combine the panade, sautéed onions, garlic, eggs, Worcestershire sauce, salt, pepper, and parsley. Whisk well.
Step 5: Add the ground beef to the bowl. Using your hands, gently mix until the ingredients are just combined. Do not overmix.
Step 6: Transfer the meat mixture to the prepared baking sheet and shape it into a 9x5 inch loaf.
Step 7: Bake in the preheated oven for 40 minutes.
Step 8: While the loaf is baking, whisk together the ketchup, brown sugar, and mustard in a small bowl.
Step 9: Remove the meatloaf from the oven and spread the glaze evenly over the top and sides.
Step 10: Return to the oven and bake for an additional 15-20 minutes, or until the internal temperature reaches 160°F (71°C).
Step 11: Remove from the oven and let the meatloaf rest for 10 minutes before slicing and serving.