1. Cook macaroni or penne according to packet instructions in well salted boiling water until al dente (slightly firm to the bite). Drain and set aside.
2. Butter a 2,5 litre (10 cup) oval, square or rectangular dish lavishly.
3. To prepare white sauce, heat milk until it is almost boiling, adding the optional mustard, bay leaves, thyme, parsley, onion and lemon peel, if using. Remove the saucepan from the stove, strain the milk through a fine sieve and set aside.
4. Melt the butter in a small heavy-based saucepan until foaming. Remove from the stove and stir in the cornflour briskly until incorporated. Return the saucepan to the stove and stir constantly over low heat until the butter and flour thicken to a paste (roux). Remove from the stove.
5. Pour in the hot strained milk in a steady stream, beating vigorously to blend thoroughly. Gather in all the bits of roux from around the edges of the saucepan.
6. Simmer (barely bubbling) over moderate heat, whisking constantly, until the sauce start to boil. Allow to boil for 1 minute, stirring constantly with a wooden spatula or spoon. Remove from the stove.
7. Add 5 ml (1 tsp) butter (optional), salt and milled black pepper and whisk briskly for a second or two, until thick and shiny.
8. Add half the grated cheese, stirring constantly until the cheese has melted.
9. Layer the cooked macaroni or penne and well-seasoned tomato slices into the greased dish. Pour over the rich, cheesy sauce. Add an extra bay leaf (optional) as well as a few pieces of butter (optional), top with remaining grated cheese, cream (optional) and breadcrumbs. Bake at 180 ºC for half an hour, or until top becomes crisp and golden.
10. Serve macaroni and cheese in heated deep, wide soup plates accompanied by a fresh green salad.