In a small bowl, combine the cocoa powder and hot water; whisk until smooth. In a medium bowl combine the flour, baking soda, baking powder, and salt and whisk to blend. Combine the butter and sugar in a medium saucepan set over medium heat. Cook, stirring occasionally, until the mixture is smooth and the butter is completely melted. Transfer the mixture to the bowl of an electric mixer and beat on medium-low speed until the mixture is cool, about 4 to 5 minutes. Add the eggs one at a time, mixing well after each addition and scraping down the sides of the bowl as needed. Blend in the vanilla and then the cocoa mixture until smooth. With the mixer on low speed, add the flour mixture in three additions alternating with the sour cream, beginning and ending with the dry ingredients and mixing each addition just until incorporated.
Divide the batter evenly between the prepared liners, filling each about ¾-full. Bake until a toothpick inserted in the center comes out clean, about 18 minutes, rotating the pans halfway through baking. Let cool in the pan about 5 to 10 minutes, then transfer to a wire rack to cool completely.
*Nutritional information is an estimate. Please consult a doctor or nutritionist for the most accurate nutritional info.