Place an already-cooked crepe in a non-stick frying pan. Crack an egg in the centre. Season with salt and pepper. Fold the sides of the crêpe inward to form a square, while leaving the yolk uncovered. Cook on that one side only, over low heat for about 5 minutes or until the egg white is cooked. If you need more than a single serving, bake in the middle of the oven at 180 °C (350 °F) for about 10 minutes on a baking sheet lined with parchment paper.