1. Cream together the fat and sugar.
2. Separate the eggs and beat the yolks, lemon rind, and juice into the creamed mixture.
3. Fold in the flour and milk.
4. Whisk the egg whites until stiff and carefully fold into the mixture.
5. Put into a greased 1 litre pie dish and bake in a moderate oven at 180°C, gas mark 4, for 40-45 minutes until firm and golden brown.
6. Serve with lemon sauce.