Peel the potatoes and cut into
Melt half the fat in a good-sized frying pan and add the onion. Cook gently for about 5 minutes until the onion is soft but not brown. Remove the onion from the pan with a slotted spoon. Add the remaining fat and raise the heat. Tip in the potato slices and fry fairly quickly to brown them. Turn the potato slices over and shake the pan occasionally. Fry the potatoes in batches if the pan is small and keep the cooked ones hot along with the onions.
Finally return the onions and all potatoes to the pan. Cook them together to heat them through and brown the onion. Sprinkle with salt and freshly milled pepper and the vinegar. Fry for a further moment, then draw off the heat. Add the finely chopped anchovies and sprinkle with parsley. Toss lightly to mix and serve hot.