Melt chocolate and butter. Place the chocolate and the butter in the top of a double boiler and melt over simmering water, stirring to blend. Set aside to cool slightly.
Prepare ramekins. Using a pastry brush, thoroughly coat the insides of 8 small baking dishes with a little melted butter.
Make batter. Beat the eggs with the sugar until light yellow and airy (about 2 minutes with a hand held mixer). Beat in the melted chocolate and butter and then the flour. Mix together until just blended completely.
Bake. Pour the batter into the serving dishes and bake for 10 to 12 minutes at 350°F. (Remember you can also put the dishes in the refrigerator and bake later in the day after allowing them to come to room temperature. That way you can time things to have a warm dessert after dinner.)
Serve. Remove from oven and allow to cool slightly. Run a knife along the outside edge of the cups, then turn out onto individual plates. Or you can just serve your moelleux in their ramekins.