1. Preheat oven to 300°F (148°C) and prepare a cupcake pan with liners.
2. Add the dry ingredients to a large bowl and whisk together. Set aside.
3. Combine the egg, buttermilk, vegetable oil and vanilla in another medium sized bowl.
4. Add the wet ingredients to the dry ingredients and mix until well combined.
5. Add the water to the batter and mix until well combined. Batter will be thin.
6. Fill the cupcake liners about half way and bake for 18-23 minutes, or until a toothpick comes out with a few moist crumbs.
7. Remove the cupcakes from oven and allow to cool for 2 minutes, then remove to a cooling rack to finish cooling.
8. To make the frosting, beat the butter in a large mixer bowl and mix until smooth.
9. Add the melted chocolate and mix until well combined.
10. Add the cocoa powder and mix until well combined.
11. Add about half of powdered sugar and 2 tablespoons of heavy cream and mix until well combined.
12. Add remaining powdered sugar and salt and mix until smooth.
13. Add remaining heavy cream as needed to get the right consistency of frosting.
14. Pipe the frosting onto the cupcakes. I used Ateco tip 844.