Step 1: In a large skillet or pot, brown the ground beef and Italian sausage over medium-high heat until fully cooked. Drain excess fat.
Step 2: Add the diced onion and garlic to the meat, sautéing for 5 minutes until translucent. Stir in tomato paste, crushed tomatoes, chicken stock, and Italian seasoning. Simmer for 30 minutes.
Step 3: In a medium bowl, combine the ricotta cheese, egg, parsley, and half of the Parmesan cheese. Mix well until smooth.
Step 4: Preheat your oven to 375°F (190°C). Spread a thin layer of meat sauce on the bottom of a 9x13 inch baking dish.
Step 5: Place a layer of noodles over the sauce. Spread a portion of the ricotta mixture over the noodles, followed by a sprinkle of mozzarella and more meat sauce.
Step 6: Repeat the layers (noodles, ricotta, mozzarella, sauce) until all ingredients are used, ending with a generous layer of mozzarella and the remaining Parmesan on top.
Step 7: Cover the dish with foil (tented so it doesn't touch the cheese) and bake for 25 minutes. Remove foil and bake for another 20-25 minutes until the cheese is bubbly and golden.
Step 8: Allow the lasagna to rest for at least 15 minutes before slicing to ensure the layers stay intact.