1. Prepare a 9x5" loaf tin by greasing it with butter and lining it with butter waxed paper.

2. Preheat the oven to 325°F.

3. Using an electric mixer cream the butter until very smooth.

4. Gradually add the sugar, beating well until very light and fluffy.

5. With and electric mixer, beat the egg yolks until light-coloured and creamy and add to them the grated rind, lemon juice, vanilla.

6. Beat this mixture well into the butter and sugar mixture.

7. Very gradually stir in the flour.

8. Beat the egg whites until they are stiff, but not dry. Fold them into the batter, a third at a time.

9. Spoon into the prepared tin and bake for 1 hour and 20 minutes, or until light golden brown.

10. Cool in the pan for 10 minutes then turn out onto a rack.

11. Carefully remove the wax paper and cool completely.

12. The cake keeps well wrapped in a brandy-soaked cheesecloth in a tin. It does not freeze well.

13. Yields 1 loaf.