Peel onion, garlic and roots, shred, and then sauté in some oil. Stir in diced tomatoes, and reduce with a sprinkle salt and pepper.

Sauté flour in oil, chill a little, and drizzle milk in, while stirring constantly. Simmer until thicken. Season with salt, pepper, and nutmeg. Toss together with grated cheese, reserving 1/5 of Parmesan cheese for covering. Dice gammon.

Grease the baking mold with the remaining oil, and, working one at a time, line with 3 lasagna sheets, tomato, gammon and cheese layers, then repeat. Bake over 392 °F (200°C) for half an hour.

Halve tomatoes, arrange over the lasagna, season with salt, pepper, and sprinkle with the remaining cheese. Bake for 10 minutes more.

When serving, garnish with greens.