Preheat the oven at 180C / 160C with fan.
Grease a baking tin of 8 inch diameter
Beat together the egg yolks, sugar and butter in a bowl using a fork or an electric mixer.
Add the greek yoghurt, lemon rind and continue mixing until smooth
Whisk the egg whites separately in a bowl
Gently fold in the flour first and then the egg whites.
Pour the mixture into the greased tin and bake for 1-1/4 hours or until the cake has risen and thoroughly cooked.
Leave to cool off on a wire rack.
For the icing
Sift the icing sugar, and mix together with the lemon juice.
Pour over the cold cake and leave to set.