Put the flour in a mixing bowl then add half the sugar and half the lemon and orange rind. Lightly beat the eggs and milk together then add to the bowl with the melted butter. Beat together until just smooth.
Spoon the mixture into the sections of a greased 12-hole deep muffin tin. Bake in a preheated oven, 190°C (375°F), Gas Mark 5, for 12–15 minutes until well risen and the tops are craggy and firm to the touch.
Make the lemon and orange syrup. Put the remaining sugar and grated citrus rind in a bowl. Strain in the fruit juices then mix together until the sugar has just dissolved.
As soon as the cakes come out of the oven, loosen the edges and turn out. Arrange in a shallow dish, prick the tops with a fine skewer or fork and drizzle the syrup over, little by little, until absorbed by the cakes. Leave to cool. The cakes are best served on the day they are made.