Make the citrus butter by mashing together the softened unsalted butter with the icing sugar, grated zest and juice of ½ orange and the grated zest of ½ lemon. Cover and chill until ready to use.
Prepare the pancake batter by sifting the flour and sugar into a large mixing bowl. Whisk the eggs and milk together in a jug then pour half onto the dry ingredients, whisking as you do until you have a thick, smooth batter. Pour the rest of the wet ingredients onto the dry and whisk until you have the right consistency of batter.
When ready to cook the pancakes, melt a knob of the citrus butter in a frying pan over a moderate heat until it stops foaming; make sure you keep some citrus butter in reserve. Add the batter and tilt the the pan so that it covers the surface evenly, adding a little more if it doesn't. Flip the pancakes once they are set on one side and cook the other side until golden and slightly crispy on the outside.
Arrange on a plate lined with a sheet of aluminium foil that is large enough to be wrapped around the pancakes loosely to keep them warm. Fold the pancakes into triangles and arrange on a serving plate.
Melt the reserved citrus butter in a saucepan over a moderate. Pour over the pancakes, garnishing with the julienned orange and lemon zest before serving.