Preheat the oven to 375°F.

Melt the butter in a large, thick-bottomed skillet, on medium heat. When the butter starts to foam, add the finely chopped onions, celery, carrot, green onions and garlic to the pan and cook for 5 minutes, stirring occasionally.

Cover the pan and cook for another 5 minutes, until the carrots are tender, stirring every so often.

Sprinkle with salt and pepper. Add the Worcestershire sauce and 1/3 cup ketchup. Cook for another minute and remove from heat to cool.

Make the meatloaf mixture:

Once the vegetables have cooled to the touch, place them in a large bowl with the ground beef, Italian sausage, eggs, breadcrumbs and parsley. Use your (very clean) hands to mix them together until everything is evenly distributed.

Place in the loaf pan, cover with remaining ketchup:

Place the meatloaf mixture into a loaf pan (either 4-x 8-inch or 5- x 9-inch) and press to make compact in the pan. Or you can form a free-standing loaf onto a rimmed baking pan. Cover the meatloaf mixture with the rest of the ketchup.

Bake for 1 hour at 375°F, or until a meat thermometer inserted into the center of the meatloaf reads 155°F.