Make the Cupcakes:

1. Preheat the oven to 350°F (175°C). Line a muffin tin with cupcake liners.
2. In a large bowl, whisk together flour, cocoa powder, granulated sugar, brown sugar, baking soda, baking powder, and salt.
3. Add buttermilk, vegetable oil, eggs, and vanilla extract, and mix until smooth. Stir in hot water or brewed coffee.
4. Fill each cupcake liner about 3/4 full with batter and bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean. Let the cupcakes cool completely on a wire rack.

Make the Ganache:

1. In a saucepan, heat the heavy cream over medium heat until steaming (but not boiling). Pour the hot cream over the chopped dark chocolate and let it sit for 2 minutes.
2. Stir the mixture until smooth. Add butter and mix until the ganache is glossy and smooth.

Assemble the Cupcakes:

1. Once the ganache has cooled slightly, chill it in the fridge for 10-15 minutes until it thickens slightly.
2. Cut a small hole in the center of each cupcake and fill with the ganache.
3. Spread or pipe more ganache on top of each cupcake to decorate.

Let the ganache set before serving, and enjoy these decadent treats!