Preheat the oven to 350F.
Melt the chocolate using water bath method. Set aside.
Cream butter and sugar. Add the melted chocolate, egg yolks and beat well.
Stir in dry ingredients and milk alternately.
In a separate bowl, beat the egg whites until soft peaks are formed. Fold into the batter.
Transfer into a greased 9" spring form and bake for about 40 minutes, or until a stick inserted into the center of the cake comes out dry.
Let the cake cool slightly, garnish with powdered sugar and chocolate shavings (optionally), and serve.