Preheat your oven to 350 degrees. Line one muffin tin with paper liners. Set aside.
Whisk together the cocoa and warm water until smooth. Set aside.
Whisk flour, baking soda, baking powder, and salt in a medium sized bowl. Set aside.
Melt the butter and sugar in a medium sauce pan over low heat. Transfer to a mixing bowl & beat for several minutes until the butter is completely cooled.
Add the eggs, one at a time, to the butter mixture. Stir until incorporated.
Stir in the vanilla and cocoa mixture until combined.
Turn the mixer speed to low. Add the dry ingredients and sour cream. Stir until all ingredients are blended.
Fill cupcake liners 3/4 full. Bake 20 minutes or until a toothpick comes out clean. Cool completely.