Season the egg with salt and pepper and beat with a little mineral water until frothy. Add the flour and beat with a dash of mineral water to form a liquid dough. Put the dough in the fridge for an hour to rise.
In the meantime, peel the onion, cut in half and cut into half rings. Wash the spring onions, remove wilted and too dirty or dry leaves and the beard. Cut the rest into fine rings.
Mix the onions together and sauté in a heated pan with a little frying fat. Remove the sweaty onions from the breakdown.
Put half of the batter in the pan, add the onions again and cover with the second half of the batter. Bake the pancake until golden brown on each side.