Preheat the oven to 350°F / 175°C and line a baking sheet with parchment paper.
Heat 1 teaspoon of olive oil in a skillet over medium heat. Cook 1 finely chopped medium onion for 5-7 minutes, until soft and golden, then let cool.
In a large bowl, whisk 2 large eggs, ⅓ cup of milk, 2 tablespoons of ketchup, 3 minced garlic cloves, 3 tablespoons of chopped parsley, 1 teaspoon of salt, 1 teaspoon of Italian seasoning, and ½ teaspoon of black pepper.
Add 900g of ground beef, ¾ cup of panko, and the onion. Mix gently until just combined, then shape into a loaf on the baking sheet.
Bake uncovered for 40 minutes. Meanwhile, for the glaze, mix ¾ cup of ketchup, 1½ teaspoons of white vinegar, 2 tablespoons of brown sugar, ½ teaspoon of garlic powder, and ½ teaspoon of onion powder.
Spread the glaze over the meatloaf and bake for about 20 minutes more, until the center reaches 160°F / 71°C. Rest for 10-15 minutes before slicing.
