Preheat the oven to 350 degrees Fahrenheit and spray a mini muffin pan generously with non-stick cooking spray. Set aside.
In a large mixing bowl, whisk together the flour, sugar, baking soda and set. Set aside.
In a saucepan, add the water, cocoa powder and butter. Heat over medium high heat and bring to a boil (stir while cooking).
Remove from heat and pour over the dry ingredients. Mix together with a hand held mixer. Add the buttermilk, eggs and vanilla extract. Mix well until combined (batter will be thin).
Place approximately 1 tablespoon of the batter into each mini muffin pans. Bake for 10-12 minutes until the tops are just set (springs back to the touch).
Remove from the oven and let sit in the pan for 10-15 minutes.
Then carefully remove the mini cakes from the loaf and place on a wire rack to cool completely.
For the Frosting:
Hear the butter, buttermilk and unsweet cocoa powder over medium heat until it comes to a low boil. Watch it closely while heating so that the buttermilk does not over boil.
Remove from the heat. Whisk in the vanilla extract and then gradually whisk in the powdered sugar (1 cup at a time) until combined, smooth and it has no lumps in the mixture.
Spoon the frosting over the mini cakes on the wire rack.
The frosting should set within 5-10 minutes and then the mini cakes are ready to serve and enjoy!
Notes
Refrigerate any leftovers in an airtight container for up to 5-6 days.