For the meat sauce (Bolognese):
Heat the olive oil in a large skillet. Sauté the onion, carrot, celery, and bell pepper over medium heat for about 4 minutes, until the vegetables are tender.
Add the ground meat and garlic and sauté for 8–10 minutes.
Deglaze with red wine or grape juice (for the non-alcoholic version) and let it simmer for about 5 minutes, until the liquid has reduced by half.
Add the pureed tomatoes, tomato paste, bay leaves, thyme, oregano, broth, salt, and pepper. Stir well and let simmer uncovered over low heat for 30–45 minutes. Finally, stir in the fresh basil.
For the béchamel sauce:
Melt the butter in a saucepan, stir in the flour, and cook for 30 seconds. Gradually stir in the milk, stirring constantly. Season to taste with nutmeg, salt, pepper, and Parmesan. Stir until the sauce thickens.
Preheat the oven to 180°C (top and bottom heat) or 160°C (convection).
Layering & baking:
Spread a little meat sauce in a baking dish (about 25×20 cm). Place lasagna noodles on top, then layer with meat sauce and béchamel sauce. Repeat until all ingredients are used up (about 3 layers), finishing with béchamel and mozzarella.
Bake in the oven for 45 minutes, until the lasagna is golden brown and bubbling. Let it rest for 5–10 minutes before serving, then sprinkle with parsley.