Add the eggs to the foaming butter, stirring continuously with a fork. When the omelette has set slightly, stop stirring. Cook, without turning, until the omelette is soft but not runny in the center. Carefully roll the omelette onto a warm plate, seam side down. If necessary, adjust the shape into a neat roll using a clean kitchen towel. (The point at which the stirring stops is the key to creating a smooth, even omelette.) A runny (baveuse) omelette will require less stirring than a firm one. A rolled omelette should have an even, smooth, uncolored surface.