Preheat your oven to 350 degrees Fahrenheit. Spray a 9 by 13 inch baking dish with cooking spray and set it aside.
Bring a large pot of water to a roaring boil. Add the lasagna noodles and cook according to the time indicated on the box. When the noodles are done cooking and have been drained, spread them on lightly greased baking sheets while you finish the sauce and make the filling. This will prevent them from sticking to each other while you are getting everything else ready.
12 lasagna noodles
While the noodles are cooking, heat a large skillet over medium heat. Add the Italian sausage, breaking it up as it cooks. Then add the onion and garlic and continue cooking until the onion is soft, about five minutes. Drain off any excess grease.
1 small yellow onion, 3 cloves garlic, 1 pound Italian sausage
Add the tomato sauce, salt, oregano, basil, sugar, red pepper flakes, and pepper to the meat mixture. Bring to a simmer and then cook on low for five minutes. You should see consistent but small bubbles. Taste and add more salt, pepper, and/or sugar to taste.
28 ounces tomato sauce, 1 tablespoon dried oregano, 1 tablespoon dried basil, 1 1/2 teaspoons sugar, 1 1/2 teaspoons kosher salt, 1/4 teaspoon red pepper flakes, 1/4 teaspoon black pepper
In a large bowl, mix the ricotta, eggs, 2 3/4 cups shredded mozzarella, and 3/4 cup shredded Parmesan cheese. (This will be divided into thirds, 1 1/3 cups for each layer.)
15 ounces ricotta cheese, 2 large eggs, 16 ounces mozzarella cheese, 1 cup Parmesan cheese
Add 3/4 cup of the meat sauce to the prepared baking dish, spreading it to coat the bottom. Top it with three lasagna sheets. Then top this with 1 1/3 cups of the ricotta mixture. Finally, add another 3/4 cup of meat sauce.
Repeat this two more times, and then top the final layer of filling with another three sheets of lasagna. In the end, you will have four layers of lasagna sheets (three for each layer) and three layers of filling (1 1/3 cups of ricotta mixture and 3/4 cup of meat sauce).
Finally, sprinkle the top of the lasagna with a combined 1 1/2 cups shredded mozzarella and 1/4 cup shredded Parmesan cheese.
Bake uncovered for 30 minutes or until the lasagna reaches an internal temperature of 165 degrees Fahrenheit. Broil for 5 minutes at the end if you would like the cheese to be browner. Let it stand for 15 minutes before slicing and serving.