Make the marinara sauce:

1. In a large pot, sweat the onions in 5 oz olive oil for 5 mins without color.
2. In a food processor, working in batches, puree the plum tomatoes, tomato paste, garlic, oregano, parsley, and the rest of the olive oil.
3. Add purees to the onions and simmer for 1 hour on low heat. Add salt and pepper and taste for seasoning.

Make the filling:

1. In a large pot over medium-high heat, cook the beef until lightly browned. Drain off the fat.
2. Add the mushrooms, onions, celery, and carrots. Cook and stir until the onions are soft.
3. Add the garlic and stir it in.
4. Add the tomato puree and tomato paste and bring to a simmer.
5. Stir in the parsley, basil, salt and pepper. Taste for seasoning.
6. Stir in 9 cups of the marinara sauce and let the mixture cool. Refrigerate until needed.

Make the lasagne:

1. Parcook the Barilla pasta for the time indicated on the package (about 8 minutes). Drainpasta and drizzle with some olive oil to prevent from sticking. Place pasta flat on sheet trays or hotel pans and cool in a blast chiller. Alternatively, cool it down in a walk-in cooler. Store in zip lock bags or sealed plastic container; refrigerate and use within several hours.
2. Spray a deep hotel pan with canola oil.
3. Place one layer of parcooked lasagna noodles in the pan.
4. Spread the noodles with about 3 cups sauce. Repeat layering the noodles and sauce, ending with a layer of noodles.
5. Scatter the cheese on top.
6. Cover with foil that has been sprayed with oil and bake at 350°F until bubbling, browned on top, and hot through.
7. Cut the pan into 24 servings. Serve immediately or reheat servings to order in a hot oven. Garnish with chopped parsley and serve with additional warm marinara sauce.