Ingredients

• 1 cup butter, softened
• 3 cups packed brown sugar
• 4 large eggs, room temperature
• 2 teaspoons vanilla extract
• 2-2/3 cups all-purpose flour
• 3/4 cup baking cocoa
• 3 teaspoons baking soda
• 1/2 teaspoon salt
• 1-1/3 cups sour cream
• 1-1/3 cups boiling water
• FROSTING:
• 1/2 cup butter, cubed
• 3 ounces unsweetened chocolate, chopped
• 3 ounces semisweet chocolate, chopped
• 5 cups confectioners’ sugar
• 1 cup sour cream
• 2 teaspoons vanilla extract