Peel and finely dice the onion and garlic. Heat the oil and sauté both in it. Dust the flour over it and sauté briefly. Deglaze with milk, stock and cream and bring to the boil while stirring. Add the cream cheese and let it melt in the sauce. Season to taste with salt, pepper and nutmeg. Cut the basil into strips, except for a few leaves for garnish, and stir into the cheese sauce.
Wash and slice the tomatoes. Dice the ham.
Layer tomatoes, ham, cheese sauce and lasagne plates alternately in a baking dish. Finish with the tomatoes and sauce and sprinkle with the parmesan cheese.
Bake the lasagne in a preheated oven at 200 ° C (electric stove) for about 45 minutes. Garnish with the remaining basil to serve.
Tip: can also be prepared very well and baked the next day.