In a large Dutch oven or pot over medium heat; sauté chopped onion in olive oil until they start to soften. Add in minced garlic, ground beef and the ground Italian sausage.
Use a wooden spoon or spatula to break up the meat, stir occasionally until the meat is fully cooked and is browned.
Measure and add in kosher salt, basil, parsley flakes and oregano.
Add in the tomato paste and stir to combine.
Crush each San Marzano tomato by hand into small pieces over the pot (to catch any juices) and add it to the pan. Add any remaining sauce from the can. I like to add a quarter cup of water to the can, swirl to remove any excess sauce and pour that in as well. Stir to combine.
Reduce the heat to low, replace the lid on your Dutch oven and let the sauce simmer for 45 minutes.
MAKE THE RICOTTA MIXTURE
In a large bowl combine the ricotta, eggs, parsley, black pepper and a half cup of both Parmesan and Mozzarella cheese.
Stir and keep in the fridge until ready to assemble the lasagna.
Assemble the Lasagna:
Preheat your oven to 375° and lightly spray a 13x9 baking pan with nonstick spray or olive oil.
Spread scant cup of sauce on the bottom of the baking pan.
Layer 1: Start with laying down 4 noodles and top with 1/3 of the ricotta mixture (spread it out). Spread out 1 to 1-1/2 cups of sauce, sprinkle with a 1/2 to 3/4 cup of Mozzarella. Just eyeball it!
Layer 2: lay down 4 more noodles and top with 1/3 of the ricotta mixture (spread), pour 1 cup of sauce (spread) and sprinkle a 1/2 to 3/4 cup of Mozzarella.
Layer 3: lay 4 noodles down, top with the remaining ricotta mixture, and 1 cup of sauce (no cheese).
Layer 4: 4 remaining noodles, the remaining sauce and sprinkle with remaining cup or so of Mozzarella.
Bake the lasagna for 30-40 minutes (rotating the pan halfway through) or until cheese is thoroughly melted and golden.
After baking let the lasagna sit for 10 minutes before cutting and serving.