Preheat the oven to 350°F. Line a 12-cup muffin pan with cupcake liners. If you have more batter, prepare a second pan.

In a large bowl, whisk together flour, cocoa powder, baking soda, baking powder, and salt.

In another bowl, whisk oil, sugar, egg, vanilla, and buttermilk until smooth.

Pour the wet ingredients into the dry, add hot coffee or water, and whisk until smooth. The batter will be thin.

Fill cupcake liners 2/3 full and bake for 20-22 minutes. Check with a toothpick for doneness.

Let cupcakes cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.

Place chopped chocolate in a bowl. Heat cream until it simmers, then pour over chocolate. Stir slowly until smooth. Chill in the refrigerator to thicken.

Beat butter until creamy. Add sugar, cream, and vanilla, then beat until fluffy. Adjust thickness and sweetness with more sugar, cream, or a pinch of salt.

Cut a circle in the center of each cupcake and fill with buttercream. Replace the top piece of the cupcake.

Spread the thickened ganache over each cupcake.

Pipe remaining buttercream on top of the ganache in your desired design.