Peheat oven to 350F and grease a 9" cake.
In a medium bowl sift flour and baking powder then add salt and mix to distribute. Set aside.
Melt the butter and chocolate in the microwave using 20 seconds increments.
Add both types of sugar to the chocolate mixture.
In a bowl beat the eggs and milk then add to the chocolate mixture.
Pour the chocolate mixture into the flour mixture and mix just until combined.
Pour the batter into the greased pan and bake for 30 minutes or until a toothpick comes out clean from the center of the cake.
Remove from the oven and allow to completely cool before adding the chocolate frosing.
Place the chopped chocolate in a medium bowl.
Over the stove, heat the cream and sugar to a simmer while stirring. Do not let it boil.
Pour the cream mixture over the chocolate and set aside for about 5 minutes. (I recommend to listen to Tom Petty's Waiting is the hardest part as a time measurement...)
Slowly stir the chocolate and cream until smooth and shiny. If you notice some unmelted chocolate bumps heat in the the microwave for 15-20 seconds.
Let the chocolate mixture cool. As it cools it will get a paste like texture.