Take a large skillet, and heat over medium-high heat. When the skillet is hot, add in 1 lb. of lean ground beef and 1 lb. of ground Italian sausage. Sauté while breaking apart the pieces with a wooden spoon, for 5 to 7 minutes, until the meat is cooked through. Transfer the meat to a food processor and pulse just until the meat is broken up into very small pieces. Transfer to a clean bowl and set this aside.

In the same skillet, heat again over medium-high heat and add in 1 tbsp of olive oil. When the oil is hot, add in 1 tbsp fennel seeds, 1/4 tsp red pepper flakes, 1 yellow onion, minced, and 6 cloves of garlic, minced, and sautéing for 2 minutes, until the onions are translucent. Add in 2 cups of spinach and 1 red bell pepper that's been diced, and continue sautéing for another 3 minutes till the vegetables are softened. Transfer this vegetable mixture into the same food processor. Pulse until the vegetables are pureed. Transfer the vegetable puree back to the skillet.

Add in one 28-oz can of whole peeled San Marzano tomatoes (including the liquid) and one 8-oz can of tomato sauce into the skillet. Stir in 2 tsp of Italian seasoning. Heat over medium heat till it's simmering. While waiting for it to heat up, continue mixing and crushing the tomatoes into pieces. When it starts to boil, cover with a lid, turn the heat down to low, and cook for 30 minutes. Throughout the 30-minute cooking time, lift the lid occasionally to stir and continue crushing the tomatoes, then replace the lid. When it's done, add the crumbled meat mixture and about 12 leaves of fresh basil that's been finely chopped. Stir till it's well combined.

While the red sauce is simmering on low, boil 12 regular lasagna noodles per box instructions till they're al dente. Fill a large pot 2/3 of the way up with water. Add salt liberally and bring to a boil. Spray baking sheets with nonstick spray to lay the noodles. Once the water is boiling, add the noodles and boil while mixing occasionally to make sure the noodles don't stick together. Drain into a colander and rinse with cold water to stop it from cooking further. Lay the noodles flat on the prepared sheet pans to prevent the noodles from sticking to each other. Set these aside.

Take a medium-sized saucepan and heat it over medium heat. Add in 4 tbsp of unsalted butter and let it melt. When the butter has melted, add in 1/4 cup of all-purpose flour and stir it into the butter. Continue to cook for 2 minutes, stirring constantly. While stirring, slowly add in 3 cups of whole milk, and continue whisking till the mixture is smooth. Add in 1/4 tsp ground black pepper. Continue cooking, stirring constantly to prevent the flour from sticking to the bottom, till it thickens enough that it coats the back of a spoon, about 5 to 7 minutes. Once it's ready, turn off the heat, divide into 4 equal portions, and set this aside.

Place an oven rack in the middle position, and preheat the oven to 350 F (175 C). Take a 9" x 13" casserole dish that's 3" high (5-quart casserole), and grease it generously with cooking spray. Add 1/2 cup of the red meat sauce on the bottom of the pan, and spread it into a thin and even layer over the bottom of the pan. This will prevent the first layer of noodles from drying up and will allow it to cook evenly. Divide the rest of the red meat sauce into 4 equal portions, and set it aside. Mix together 1 lb of shredded mozzarella cheese and 8 oz of freshly-grated parmesan cheese, mix them together in a bowl, and divide into three equal parts.

On top of the initial thin layer of red sauce, lay three of the al dente lasagna noodles. Spread one-fourth of the red meat sauce over the noodles, then spread one-fourth of the béchamel white sauce then one-third of the cheese mixture, spreading all of them to the edges. Top with another layer of three noodles, then one fourth of red meat sauce, one fourth of white béchamel sauce, then one-third of cheese mixture. Repeat with another layer of three noodles, red meat sauce, white béchamel sauce, and last one-third of the cheese mixture. Then add the final layer of three noodles, last one-fourth of red meat sauce, and last one-fourth of white béchamel sauce. For the final layer, add an extra thick layer of cheese on top by mixing 8 oz of shredded mozzarella cheese and 4 oz of freshly-grated parmesan cheese, then sprinkling it evenly over the béchamel sauce, making sure it goes all the way to the sides of the dish. Take a piece of aluminum foil that’s big enough to cover the top of the dish. Spray one side with cooking spray to prevent the cheese from sticking to the foil. Then with the oiled side facing down, cover the dish with the aluminum foil, sealing the edges tightly.

Bake with the aluminum foil cover at 350 F (175 C) for 30 minutes. Then remove the foil and continue baking for another 15 to 20 minutes, or until the lasagna is hot and bubbling and the top layer of cheese is completely melted and slightly browned. Let it rest for 20 minutes at room temperature before serving, so the layers can set before slicing. Garnish with an optional 3 fresh basil leaves that have been finely chopped. Slice into 12 equal servings. Enjoy!