Combine all the ingredients except the oil in a medium bowl and mix together gently with a fork until a soft dough forms. Add a little more flour if the dough feels too sticky. Turn the dough out onto a lightly floured bench. Using floured hands, shape the dough into a long fat sausage, then cut the sausage into 4. Roll each to the thickness of your thumb and until smooth and even in length. Use a sharp knife dipped in flour to cut the dough into small, walnut-sized pieces. Transfer the gnocchi with a fish slice to a baking tray lined with a clean tea towel dusted lightly with flour.

Bring a large saucepan of heavily salted water to the boil. Get a large bowl of iced water ready to plunge the gnocchi into when cooked. Gently slip a quarter of the dumplings into the boiling water, leave for 1 minute, then stir gently with a wooden spoon.