Beef Stroganoff

150 ml/1/4 pint plain low-fat yogurt
1 teaspoon Dijon mustard
salt
freshly ground black pepper
450 g/1 lb beef fillet or sirloin steak, trimmed
2 large onions, peeled and chopped
about 150 ml/1/4 pint beef stock
3 dessertspoons dry sherry
100 g/4 oz mushrooms, sliced

Mix the yogurt, mustard, salt and pepper together and set aside. Cut the steak carefully into wafer thin strips.

Put the onions in a saucepan with just enough stock to cover the bottom of the pan. Add the sherry and cook gently for about 10 minutes until softened, adding more stock if necessary. When the onions are transparent, add the beef and mushrooms and turn up the heat.

Cook for 1 minute, stirring rapidly. (If the beef is not cut wafer thin, the cooking time will be longer - about 3 to 5 minutes.) Remove from the heat and stir in the yogurt mixture. Serve immediately while piping hot.

SERVES 4