For the Cupcakes: Preheat your oven to 350°F (175°C). Line a mini muffin tin with mini cupcake liners.

1. In a medium bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt. Set aside.
2. In a large bowl, beat the softened butter and granulated sugar until light and fluffy, about 3-4 minutes.
3. Add the eggs one at a time, mixing well after each. Stir in vanilla extract.
4. Gradually add the dry ingredients to the wet ingredients, alternating with the buttermilk. Start and end with the dry ingredients. Mix until just combined.
5. Gradually add the hot water to the batter, mixing until smooth.
6. Spoon the batter into the mini cupcake liners, filling each about 2/3 full.
7. Bake for 10-12 minutes, or until a toothpick comes out clean.
8. Let the cupcakes cool in the tin for 5 minutes before transferring to a wire rack to cool completely.
9. For the Chocolate Buttercream: Beat the softened butter until smooth and creamy.
10. Sift together the powdered sugar and cocoa powder, then add to the butter and mix until smooth.
11. Add heavy cream, vanilla, and a pinch of salt, then beat until fluffy.
12. Once cupcakes have cooled, pipe or spread the chocolate buttercream onto each mini cupcake.