Pre‑heat your pot: Heat the olive oil in a large pot over medium heat. Add the diced onion and minced garlic. Sauté until the onion begins to soften and the garlic is aromatic—several minutes.

Brown your meats: Add the Italian sausage and ground beef. Break them up and cook until fully browned. Drain off excess fat, leaving a bit behind for flavour and moisture.

Build your sauce: Into the browned meat add the whole tomatoes (with their juice), the tomato sauce or marinara, Italian seasoning, red pepper flakes, salt and black pepper. Stir to combine. Simmer for about 25–30 minutes, allowing the flavours to meld. After this time, remove 3–4 cups of the meat‑tomato sauce into a separate bowl and set aside to cool slightly.

Prepare the oven & cheese‑pasta mix: While the sauce simmers, pre‑heat your oven to 375 °F (≈ 190 °C). In a separate bowl mix together the ricotta cheese, 2 cups of the grated mozzarella, the parmesan, the egg, and a little salt and pepper. Stir just a couple of times; you don’t need to smooth it totally—some lumps are fine.

Cook your pasta: Drain the ziti or mostaccioli when it’s just short of al dente (it will finish baking later). Rinse under cool water to stop the cooking and help it handle gently.

Combine pasta with cheese mixture & sauce: Pour the drained pasta into the bowl with the cheese mixture and gently toss so the pasta gets coated (but don’t blend completely smooth—visible cheese pockets are a plus). Then add the reserved cooled meat‑tomato sauce and toss again until combined.

Assemble & bake: In a large casserole dish, add half of the coated pasta mixture. Spoon half of the remaining sauce over it, then sprinkle half of the remaining grated mozzarella cheese. Add the second layer: the rest of the pasta, then the rest of the sauce, then the remaining mozzarella on top. Bake in the oven until bubbling and the cheese is melted and golden—about 20 minutes.

Finish & serve: Remove from the oven and let stand for about 5 minutes before serving (this helps it set a bit so portions hold). Garnish with freshly chopped parsley right before serving.