Preheat oven to 350°F. Grease and flour a bundt pan.
Combine the baking chocolate, butter and boiling water in a small bowl; stir until chocolate and butter are melted.
In a large bowl, combine brown sugar, flour, baking soda and salt. Gradually add chocolate mixture to the dry ingredients; blend well. Add eggs, sour cream and vanilla; beat one for one minute at medium speed. Pour into prepared bundt pan.
Bake for approximately 40 minutes or until a toothpick comes out clean.
Cool in the pan on a cooling rack for 10 minutes. Invert the pan onto the cooling rack and let cool the rest of the way.Top with powdered sugar.
The nutrition information provided are only estimates based on an online nutritional calculator. This is not a comprehensive list of all the nutrients in the recipe (i.e., does not include vitamins, cholesterol, etc). I am not a certified nutritionist. Please consult a nutritionist or doctor for accurate information and any dietary restrictions and concerns you may have.