Preheat oven and make breadcrumbs: Preheat oven to 375°F. Pulse bread in a food processor until finely ground. (You should have about 2 ½ cups breadcrumbs.) Transfer to a medium bowl.
Pulse vegetables in food processor: Pulse garlic, onion, celery, carrot, and parsley in food processor until finely chopped. Add to breadcrumbs.
Add meats, ketchup, mustard, Worcestershire, and mix by hand: Add meats, egg, ¼ cup ketchup, the mustard, Worcestershire sauce, 1 teaspoon salt, and ½ teaspoon pepper; mix together using your hands.
Place meatloaf mixture in pan: Transfer mixture to a 5-by-9-inch loaf pan.
Mix ketchup and sugar and brush on meat: Stir together remaining ½ cup ketchup and the brown sugar until smooth; brush onto meat.
Bake: Set pan on a rimmed baking sheet, and bake until an instant-read thermometer inserted into the center reaches 160°F, about 1 hour 20 minutes. Let cool slightly before serving.
