1. Sieve the flour.
2. Cream the fat and sugar, beat in the lemon rind and egg yolk.
3. Work in the flour, adding enough water to make a soft dough.
4. Roll out on a lightly floured surface about 1/8 in. thick.
5. Cut into rounds or fancy shapes with cutters.
6. Bake in a moderately hot oven (375°F - Gas Mark 5).
7. Lift carefully on to a wire tray with a palette knife. Leave until cold and crisp.
8. Dredge with castor sugar.