For the purée, combine passata with EVOO, salt and basil.
For the marinara, heat a Dutch oven or saucepot over medium to medium-high heat. Add olive oil, 4 turns of the pan, along with the onions, carrot, celery, garlic, sugar, salt and white pepper, oregano, red pepper and thyme. Cook to soften, 10 minutes. Add tomato paste, stir 1 minute, then add wine and reduce by half. Add tomatoes, passata and basil, and simmer 20-30 minutes.
For the meat sauce, heat olive oil in a large skillet over medium-high heat. Add meat and crumble and brown. Add fennel, red chili flakes and salt. Combine the parsley with the garlic then stir into meat. Add about half of the marinara sauce to the beef. Add all of the toasted garlic breadcrumbs to the meat sauce.
For the white sauce, melt butter in small saucepan over medium heat. Whisk in flour then add wine and reduce by half. Add milk, season with salt and white pepper, and thicken. Stir in grated cheese and remove from heat.
In a bowl, combine spinach, ricotta, egg yolks, salt, pepper and nutmeg. When white sauce has cooled, combine it with the spinach and ricotta.
In a medium-size, nonstick skillet, bring 1/8 inch of water to a boil. Add sausages and reduce to a simmer. Cook sausages through, letting the water evaporate. Add a drizzle of olive oil and brown casings. Remove, cool and slice very thin on a bias.
Preheat oven to 350°F with a rack in the center.
Butter a lasagna pan. To assemble lasagna, ladle some of the tomato-basil purée on the bottom of the pan then build layers of pasta, 1/2 of the meat sauce, pasta, all of spinach and white sauce mixture, pasta, sausage, plain marinara, pasta, remaining meat sauce, pasta and tomato-basil purée. Top with mozzarella and grated cheese.
Bake covered with foil for 45 minutes then remove foil and bake uncovered 15-20 minutes until golden and bubbly. Let sit 20 minutes before cutting.
Serve with extra marinara and warm Italian bread at the table.