Heat the oven to 350°F and line a 9-inch loaf pan with parchment paper. Set aside.
In a large bowl, combine the beef and sausage together. Add ½ cup marinara sauce, onion, ¼ cup parmesan cheese, bread crumbs, egg, garlic, Worcestershire sauce, Italian seasoning, and salt, and mix well.
Place a piece of parchment paper or saran wrap onto your workspace. Place your pan length wise at the end of your workspace.
Press your meat out in a rectangular shape, making sure it is not wider than your pan. Lay your prosciutto out on your meat, then place the spinach over the meat. Spread half of the mozzarella cheese over the spinach.
Roll the meat up into a roll and place seam side down in the prepared loaf pan.
Bake for 45 minutes. Remove and top meatloaf with the remaining marinara sauce and mozzarella. Bake for an additional 15 to 20 minutes, until the sauce is bubbly and the cheese is melted and golden.
Let meatloaf rest for 10 minutes before slicing and serving. Top with remaining Parmesan cheese and parsley, if desired.
Notes
Freeze Whole Meatloaf: Assemble the raw meatloaf as usual in a disposable loaf baking pan. Cover with foil and place it in a freezer-friendly bag. Freeze for up to 3 months. Thaw overnight in the fridge and then bake as usual.Store Leftovers: Place cooled meatloaf in an airtight container and store in the fridge for up to 5 days.Reheat: Microwave in 30-second intervals, until warm. You can also cover with foil and heat in the oven at 350°F for about 15 minutes.Prep Ahead: Assemble the meatloaf a day in advance, but don’t bake it. Cover it in foil and refrigerate it for up to 48 hours. Then bake it the next day when you’re ready for dinner!Add More Veggies: You can add 1/4-1/2 cup thinly sliced bell peppers, chopped artichoke hearts, or mushrooms for even more flavor.Add Heat: Add red pepper flakes to taste, or use a spicy marinara sauce, for an added kick of heat.