Ingredients

• 4 slices white sandwich bread
• 1 small yellow onion
• 1 stalk celery
• 3 cloves garlic
• 1 medium carrot
• 1 small bunch fresh parsley
• 4 ounces low-moisture mozzarella cheese, shredded (about 1 cup)
• 1 ounce Parmesan cheese, finely grated (about 1/2 firmly packed cup grated on a Microplane or 1/3 cup store-bought)
• 1 1/2 pounds lean ground beef (90% lean)
• 1 pound ground pork
• 1 (24-ounce) jar store-bought or homemade marinara sauce (about 3 cups), divided
• 1 large egg
• 2 teaspoons Worcestershire sauce
• 2 teaspoons kosher salt
• 1 teaspoon Italian seasoning
• 1/2 teaspoon freshly ground black pepper
• 1/4 teaspoon red pepper flakes

1. Arrange a rack in the middle of the oven and a second rack in the upper third and heat the oven to 375°F.
2. Tear the ​​4 slices white sandwich bread into small pieces and place in a food processor fitted with the blade attachment. Pulse until finely ground, about 10 (1-second) pulses. Transfer to a large bowl.
3. Prepare the following, adding each to the food processor as you go: Coarsely chop 1 small yellow onion, 1 celery stalk, and 3 garlic cloves. Peel and coarsely chop 1 medium carrot. Pick the leaves from the 1 small bunch fresh parsley until you have 1/2 packed cup; finely chop 2 tablespoons of the leaves and refrigerate for garnish, and add the remaining leaves to the food processor. Pulse until everything is finely chopped. Transfer to the bowl with the bread crumbs.
4. Grate 4 ounces mozzarella cheese on the large holes of a box grater (about 1 cup) and reserve for sprinkling. Grate 1 ounce Parmesan cheese on the small holes of the box grater (about 1/2 packed cup).
5. Add the Parmesan, 1 1/2 pounds lean ground beef, 1 pound ground pork, 1/4 cup of the marinara sauce, 1 large egg, 2 teaspoons Worcestershire sauce, 2 teaspoons kosher salt, 1 teaspoon Italian seasoning, 1/2 teaspoon black pepper, and 1/4 teaspoon red pepper flakes. Mix with your hands until well combined. Transfer to a broiler-safe 9x13-inch baking dish and use your hands to shape into a 6x13-inch loaf.
6. Bake on the middle rack until cooked through (an instant-read thermometer inserted into the center should register at least 165ºF), 55 minutes to 1 hour and 5 minutes.
7. Remove from the oven and carefully spoon off or drain any excess fat in the baking dish. Switch the oven to broil on high. Spoon 1 cup of the marinara sauce over the top of the meatloaf. Spoon the remaining 1 3/4 cups marinara around the sides of the meatloaf. Sprinkle the meatloaf with the reserved mozzarella.
8. Broil on the upper rack until the cheese is melted and golden-brown, about 3 minutes. Let cool for 10 minutes. Sprinkle with the reserved parsley, slice, and serve with marinara spooned over the top.