heat butter in and sugar in a deep frying pan over low heat, stirring occasionally, until the sugar begins to dissolve. turn up the heat and bubble fast until the mixture just starts to go brown and caramelise ( 4 minutes).
Pour in juice and zests then bubble for 3-4 minutes to thicken slightly. Add the liqour, flame for a few seconds.
Put one crepe into the sauce and coat well then fold in 4 like a handkerchief.Push to one side of the pan and continue with the rest. Serve 2-3 crepes per person.