Use a peeler to remove thin layers of orange peel, trying to not remove too much pith. Cut the peels in half so they're not too long and then slice them thinly.
Add the butter, peels and orange juice to a pan and place over medium heat until it begins o boil.
Add the liqueur and flambée it or just let it simmer.
Let the sauce boil until it thickens slightly. If you want a boozy kick, add more liqueur at this point.
Cover the crepes with the hot sauce and serve immediately.