Beat butter and sugar to a cream

Stir in egg yolks one at a time and then add the flour sifted with baking powder and pinch of salt

Add vanilla essence and mix well

Spread ½cm/¼inch thick on well-greased oblong tin about 25cm/10inch x 22cm/9inch

Sprinkle with chopped walnuts

Beat the 2 egg whites until stiff

Lightly mix in brown sugar and spread over the nuts

Bake for half an hour in a moderate oven (180°C/350°F/Gas mark 4)

Leave till cold and cut into squares