Use this recipe to make our Meatloaf Sandwich.
Heat oven to 400 degrees. Place bread in bowl of a food processor; pulse until fine crumbs form. Transfer to a bowl; add ground beef.
Place onion, garlic, celery, carrots, and parsley in food processor; pulse until finely chopped. Add to meat mixture; combine using your hands. Add egg, 1/2 cup ketchup, 2 teaspoons dry mustard, the salt, and pepper; combine thoroughly using your hands. Place in an 8 1/2-by-4 1/2-by-2 1/2-inch loaf pan.
Combine remaining 1/4 cup ketchup, remaining 2 teaspoons dry mustard, and the brown sugar in a bowl; stir until smooth.
Brush mixture over meatloaf; place in oven with a baking pan on rack below to catch drippings. Cook until a meat thermometer inserted into middle reaches 160, about 90 minutes. If top gets too dark, cover with foil, and continue baking.