Preheat oven to 180 degrees C and grease a heart-shaped cake tin well.
Melt the chocolate and butter together in the microwave or with a double boiler over simmering water. Place in a mixing bowl and add flour, sugar and egg yolks. Mix well.
Beat the egg whites until stiff and fold into the batter. Pour batter in the tin and bake 25 minutes. Let cool and ice, if desired.