Preheat the oven to 350°.
Coat a 12-cup Bundt pan with cooking spray. Mix the cocoa and chopped chocolate in a heatproof bowl. Pour boiling water over the chocolates and stir to melt. Let the mixture stand to cool (about 2 to 3 minutes).
Meanwhile, combine the flour, salt, and baking soda in a medium bowl. Cream the butter, brown sugar, vanilla until creamy in a large bowl. Add the eggs to the butter mixture and blend well. Fold the sour cream into the cooled chocolate mixture until incorporated. Add the flour mixture and the sour cream chocolate mixture to the butter mixture and blend well. Add the chocolate chips to the batter and stir to incorporate.
Pour the batter into the prepared pan and bake for 55 minutes or until an inserted toothpick comes out clean. Cool the cake slightly before removing from the pan. Sprinkle the cake with powdered sugar and serve.
*Optional – may serve with whipped cream or chocolate ganache.