Boil the potatoes, with their skins on, until tender.
Heat the olive oil in a frying pan and fry the onion until golden.
Peel the potatoes while they are still hot, then pass the potatoes, onion and Swiss chard through a food mill or ricer. Place the mixture in a bowl.
Stir in the egg and flour to form a soft, pliable dough.
Divide the dough into pieces the size of a small fist and roll them out into lengths about 2cm/¾in thick. Cut the lengths into 2cm/¾in long pieces. The gnocchi can be frozen at this stage; spread them out on a well-floured tray and put them in the freezer. When frozen, shake off any excess flour and put them in a bag. Use within 3 months.
To cook, boil the gnocchi in salted water for about two minutes (allowing 1-2 minutes extra cooking time if cooking from frozen). When they're cooked they will bob up to the surface.
Drain well and serve immediately with the sauce of your choice.
Type the ingredients you want to use, then click Go. For better results you can use quotation marks around phrases (e.g. "chicken breast"). Alternatively you can search by chef, programme, cuisine, diet, or dish (e.g. Lasagne).