Layers of pasta, meat sauce, and molten mozzarella. Lasagna is the high calorie dinner that gets better each day as leftovers — if it survives that long.
Heat a large saucepan over medium heat and add olive oil. Sauté diced onion, carrot, and celery for 4–5 minutes until softened.
Increase heat to medium-high and add ground beef and sausage. Cook, breaking apart with a spoon, until browned and most moisture has evaporated—about 8 minutes. Add garlic; cook 1 minute.
Stir in tomato paste; cook for 2 minutes to caramelize. Add crushed tomatoes, oregano, basil, 1.5 tsp salt, and 0.5 tsp pepper. Lower to a gentle simmer, cover, and cook for 50 minutes, stirring every 10 minutes.
Meanwhile, cook lasagna noodles in a large pot of boiling salted water until just al dente. Drain and lay flat on a towel to prevent sticking.
In a bowl, combine ricotta, egg, half the Parmesan, and a pinch of salt and pepper. Preheat oven to 375°F (190°C).
Assemble the lasagna: Spread a thin layer of meat sauce in a 9x13-inch baking dish. Layer noodles, a third of the ricotta mixture, sauce, and mozzarella. Repeat for three layers, finishing with sauce and remaining mozzarella and Parmesan.
Cover with foil (tent to avoid cheese contact) and bake for 30 minutes. Remove foil and bake another 20 minutes, until bubbling and golden. Cool for at least 20 minutes before slicing.