Heat 100 ml extra virgin olive oil in a large saucepan over medium heat. Blend 2 yellow onions and 3 cloves garlic into a smooth paste, add them to the pan with 1 tsp salt and ½ tsp freshly ground black pepper, and sauté until translucent.
Blend 1 red bell pepper into a paste and add it to the pan. Cook for a few minutes. Blend 2 carrots into a paste, add them, and cook until the vegetables soften.
Add 1 kg ground pork with the remaining 1 tsp salt and ½ tsp freshly ground black pepper. Cook until the meat is browned, breaking it up with a spoon.
Stir in 700 g passata and cook for a few minutes. Pour in 100 ml white wine, then add 2 bay leaves, 3 cloves, ½ tsp thyme, and 1 tsp dried oregano . Add 100 ml water, bring to a simmer, cover, and cook on low heat for at least 1½ hours, stirring occasionally.
Melt 125 g butter in a saucepan over medium heat. Add 70 g wheat flour 00 and whisk over low heat for about 3 minutes until a smooth roux forms. Gradually pour in 1 l whole milk while whisking constantly. Season with ¼ tsp salt, ⅛ tsp freshly ground black pepper, and ⅛ tsp nutmeg, and cook until the sauce thickens.
Spread a thin layer of béchamel on the bottom of a baking dish. Add a layer of 12 lasagna sheets, oven-ready, then béchamel, Bolognese, and a sprinkle of 100 g Parmesan cheese and 100 g Mozzarella cheese. Repeat the layers until everything is used, finishing with béchamel and Parmesan on top.
Cover the baking dish with aluminum foil. Cover with aluminum foil and bake in a preheated oven at 390°F / 200°C (375°F convection / 190°C fan) for 15 minutes. Remove the foil and bake for another 10 minutes until golden and bubbly.
Let the lasagna rest for a few minutes before slicing so the layers set properly.
Notes
Blend the Vegetables Well: I like blending the onion, garlic, red pepper, and carrots into a smooth paste because it helps the sauce cook down evenly and gives it a softer texture.Let the Sauce Simmer Slowly: Cooking the Bolognese gently for about 1½ hours builds deeper flavor in the meat sauce.Whisk the Béchamel Steadily: I keep whisking while adding the milk so the sauce stays smooth and thickens without lumps.Let the Lasagna Rest: Allowing it to sit for a few minutes after baking helps the layers settle and makes slicing easier.