Preheat your oven to 350 degrees. Spray a 9 by 13 inch baking dish with cooking spray and set 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 in 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 together the ricotta, eggs, 2 3/4 cup shredded mozzarella, and 3/4 cup shredded Parmesan cheese. (This will be divided into thirds, 1 1/3 cup 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 cup 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 cup of ricotta mixture + 3/4 cup of meat sauce).
Finally, sprinkle to the top of the lasagna with a combination of 1 1/2 cups shredded mozzarella and 1/4 cup shredded Parmesan cheese.
Bake uncovered for 30 minutes. Broil for 5 minutes at the end if you would like the cheese to be more browned. Let stand for 10 minutes before slicing and serving.