Preheat oven to 400°F. Lightly grease a broiler pan (oven grill pan), or regular baking sheet.
In a large bowl, soak bread slices in the milk, pressing them down with your fingers. Allow to soak while sautéing the onion.
Heat the oil in a small pan over medium heat and sauté the onion until soft and translucent (about 5 minutes). Add the garlic and sauté for a further 30 seconds until fragrant. Set aside and allow to cool slightly.
Mash the soaked bread with a fork to break up large pieces. Add in the onion/garlic, beef, parmesan, eggs, parsley, tomato paste, Worcestershire sauce, mustard, salt and pepper. Mix with your hands until everything is just combined (try not to over-mix).
Scoop meat mixture into a loaf pan, pressing down lightly to form into a loaf shape. Turn out onto prepared tray.
In a smaller bowl, mix together all the ingredients for the glaze. Spread half of the sauce evenly over the top; reserve the renaming sauce for later.
Bake the meatloaf for 50 minutes, then spread half of the remaining sauce over the top. Return to the oven and bake for a further 20 minutes.
Allow to rest for 10 minutes before slicing. Mix any pan juices with the remaining sauce to serve!
