1. Grease two large baking sheets.
   
2. Cream the butter and sugar until pale and fluffy. Add the egg yolks and beat well.
   
3. Stir in the flour and grated lemon rind and mix to a fairly firm dough with a round-bladed knife. 4 Turn out on to a lightly floured surface and knead lightly. 5 Roll out to about 5 mm (1/4 inch) thick. Cut into rounds with a 6 cm (2 1/2 inch) fluted cutter and place on the baking sheets. 6 Bake in the oven at 180°C (350°F) mark 4 for about 15 minutes, until firm and a very light brown colour.

VARIATION
Add 50 g (2 oz) chopped dried fruit to the mixture with the flour.