Preheat your oven to 350°F (175°C) and line a rimmed baking pan with foil. Lightly coat the foil with cooking spray to prevent sticking.

In a skillet, melt a tablespoon of butter over medium heat. Add the diced medium onion and sauté for about 5 minutes, or until they become translucent and tender.

In a large mixing bowl, combine two beaten eggs, half a cup of milk, and one cup of Italian breadcrumbs. Allow this mixture to sit for about 5-10 minutes.

Once the onions have cooled, add them to the breadcrumb mixture along with one pound of lean ground beef, a quarter cup of ketchup or chili sauce, two teaspoons of Italian seasoning, two tablespoons of chopped parsley, and a pinch of kosher salt and black pepper.

Transfer the meat mixture to your prepared baking pan and shape it into an 8"x4" loaf. Bake in the preheated oven for 40 minutes.

While the meatloaf bakes, prepare the topping by mixing a quarter cup of chili sauce with an equal amount of ketchup and one tablespoon of brown sugar if desired.

After 40 minutes, carefully remove the meatloaf from the oven, spread the topping over the meatloaf, and return it to the oven for an additional 15-30 minutes.

Once baked, remove the meatloaf from the oven and allow it to rest for 10 minutes before slicing.