Pour the orange juice into a saucepan, and add the zest, butter and sugar. Bring to the boil, and then turn the heat down to a simmer, cooking for a further 10 to 15 minutes until the sauce becomes syrupy.
Fold the crepes into quarters and then arrange them in a large pan, or any oven-proof dish, slightly overlapping in a circular pattern.
Pour over the warm syrup and then gently heat the crepes through for about 3 minutes over a low heat.
Warm the orange liqueur of your choice in the emptied but still syrupy saucepan. When the crepes are hot in the orange sauce, pour over the liqueur and set light to the pan to flambe them. Serve immediately spooning crepes and sauce onto each plate.