Put the potatoes in a large pan with just enough water to cover them and crumble in the stock cubes. Bring to the boil, then cover and cook for 5 mins. Add the zucchini/.ourgettes, put the lid back on and cook for 5 mins more.
Take off the heat, then stir in the cheese and season with the nutmeg, salt and pepper. Whizz to a thick soup, adding more hot water until you get the consistency you like, then add the majority of the chives.
Serve scattered with extra grated cheddar, chives and nutmeg or pepper. Or cool and freeze in freezer bags or containers with good lids for up to 3 months.