Preheat the oven to 350. Cut the tomatoes in half lengthways. Place on a rack over an oven tray, season well with salt and pepper and cook for 1 hour, or until they have dried out slightly. Remove from the oven, drizzle with the balsamic vinegar and top with the shredded basil leaves. Place on a serving platter and set aside.
Meanwhile, cook the macaroni in a large saucepan of boiling salted water until just tender and drain. Melt the butter in a large saucepan over low heat, Add the onion and garlic and cook for 5 minutes, or until softened. Stir in the flour and cook over a low heat for 2 minutes. Remove from the heat and gradually whisk in the milk. Return to the heat and stir constantly until the sauce boils and thickens. Reduce the heat and simmer for 2 minutes. Remove from the heat, stir in the mustard, Cheddar, cottage cheese and parsley. Add the macaroni and mix gently.
Spray a 1.5 liter (6 cup/53 fl oz) ovenproof dish with olive oil. Spoon the mixture into the dish. Combine the breadcrumbs, nutmeg and Parmesan and sprinkle over the top. Bake for 25 minutes, or until golden and bubbling. Serve with the roast tomato salad, a mixed green salad and thick slices of wholegrain bread.