Separate the eggs. Mix the egg yolk, flour and milk into a pancake batter that is not too thick. Beat the egg whites with the sugar until stiff.
Heat some butter in a pan over medium heat and pour in half of the batter. Bake the pancake until golden brown on the first side, turn over and immediately reduce the heat. Pile half of the egg whites on one half of the pancake and fold the cake in two. Bake gently until golden brown, turning once, the egg whites also set.
Slide onto a plate and keep warm in the oven at around 70 degrees until the second pancake is baked. Dust with powdered sugar, serve with fruit if necessary.