- 1 cup butter softened
- 3 cups packed brown sugar
- 4 large eggs
- 1 tablespoon vanilla extract
- 2 2/3 cups all-purpose flour
- 3/4 cup unsweetened cocoa powder
- 3 teaspoons baking soda
- 1/2 teaspoon salt
- 1 1/3 cups sour cream
- 1 1/3 cup boiling water
- 1/2 cup butter
- 3 ounces unsweetened baking chocolate chopped
- 3 ounces semi-sweet baking chocolate chopped
- 5 cups powdered sugar
- 1 cup sour cream
- 1 teaspoon vanilla extract
- Preheat oven to 350 degrees F. Grease a 10x15 inch (4-4.5 quart) glass baking dish with non-stick cooking spray.
- In a large mixing bowl, cream together the butter and brown sugar until light and fluffy. Add eggs, one at a time, beating well after each addition. Stir in vanilla extract.
- In a separate bowl, mix together flour, cocoa powder, baking soda, and salt. Whisk to combine. Add the wet mixture and sour cream to the dry ingredients and beat with an electric mixer just until well blended. Add the boiling water then stir until combined.
- Pour the batter evenly into the prepared baking dish. Bake at 350 degrees for 40-45 minutes until a toothpick inserted into the center of the cake comes out clean. Set the cake aside to cool.
- Microwave the butter in a microwave safe bowl just until melted. Stir in the semi-sweet and unsweetened chocolate. Microwave in 30 second intervals, stirring between each interval, until the chocolate is melted.
- In a large mixing bowl, combine the melted chocolate and butter mixture, powdered sugar, sour cream, and vanilla; beat with an electric mixer until smooth.
- Spread the frosting evenly onto the cooled to room temperature cake.