Preheat oven to 425° F.
Grease and line with wax paper a 9x5x3 loaf pan.
Melt chocolate and beat in butter with a spoon or spatula.
Beat egg whites with a hand mixer to stiff peaks; set aside. With same beaters beat egg yolks until thick and light in color.
Slowly add the sugar, beating constantly. Add the flour and beat until just combined. Stir egg yolk mixture into chocolate mixture, then fold egg whites into this mixture. You will have some egg whites still showing.
Pour batter into prepared pan. Reduce oven heat to 350°F and bake 25 minutes.
Let cool completely in pan. Cake will settle like a cheesecake. Turn out. Refrigerate for 4 hours until well chilled. Decorate with abandon!