Chill the creme eggs in the fridge for one hour then unwrap and carefully poke the edge of a sharp knife into the seam of each egg and gently saw until they fall apart (a serrated knife is a good option for this). Keep a few spare eggs in supply as it's inevitable that one or two won't cut perfectly. (Top tip: Quickly hide the evidence of those little fails by eating them. Nobody will be any the wiser).