Butter a 1.5-2 litre (2¾-3½ pint) gratin dish and heat the oven to 190°C/375°F/gas mark 5.
In a blender whizz the cottage cheese, mustard, cayenne, nutmeg and some salt and pepper.
Tip into a large bowl. Keep back about 100g (3½oz) of the cheddar and add the rest to the cottage-cheese mixture along with the parmesan (if using) and the milk.
Stir in the raw macaroni and pour into the dish.
Cover with foil and bake for 30 minutes. Take off the covering, stir and sprinkle the remaining cheese on top. Return the dish – uncovered – to the oven and bake for a further 30 minutes.
Leave to cool for five to eight minutes before tucking in; it will be molten hot in the middle.
Serve with a big green salad dressed with a mustardy vinaigrette.