Step 1

Preheat oven to 375°F with racks in center and upper third positions. Lightly grease a 13- x 9-inch rimmed baking sheet with cooking spray; sprinkle ½ cup of the panko evenly on bottom of baking sheet. Stir together onion, Parmesan, milk, parsley, garlic, eggs, Italian seasoning, Worcestershire sauce, and remaining 1 cup panko in a large bowl to combine. Add beef, pork, and 1 tablespoon of the salt to mixture, stir to combine. Transfer meatloaf mixture to baking sheet, and press into an even layer out to edges of baking sheet.

Step 2

Whisk together ketchup, brown sugar, vinegar, black pepper, and remaining 1 teaspoon salt in a medium bowl. Spread ketchup mixture evenly over meatloaf. Bake on center rack in preheated oven until cooked through and a thermometer inserted in thickest portion registers 160°F, about 40 minutes. Remove from oven, and turn oven to broil. Broil on top rack until glaze becomes caramelized, about 3 minutes. Remove from oven, and let stand 5 minutes before serving.