Buckwheat crepes are slow to brown so you should not have any problems if you reduce the heat to low before adding the egg and you spread the egg white as much as possible on the crepe so that it cooks faster. Folding the crepe back onto the white (once you add the cheese and ham), also accelerates the cooking. This method works well even with a crepe that has already been browned on both sides. Obviously if you are adding the filling as you make the crepes, add the egg right after turning the crepe over. I hope this helps! Anne-Laure