Preheat oven to 375 degrees F (190 degrees C) and lightly butter or line 12 muffin cups with paper liners.

Cupcakes: In a small bowl stir until smooth the boiling hot water and the cocoa powder. Let cool to room temperature.

In a bowl, whisk together the flour, baking powder, and salt. Set aside.

Then in the bowl of your electric mixer, or with a hand mixer, cream the butter and sugar until light and fluffy. Add the egg and beat until smooth. Beat in the vanilla extract. Add the flour mixture and beat until incorporated. Then add the cooled cocoa mixture and stir until smooth.

Evenly fill the muffin cups with the batter and bake for about 17-20 minutes or until risen, springy to the touch, and a toothpick inserted into a cupcake comes out clean. Remove from oven and place on a wire rack to cool. Once the cupcakes have completely cooled, frost with icing. If you want flat topped cupcakes then slice off the dome of each cupcake, with a sharp knife, before frosting. 

Chocolate Frosting: Melt the chocolate and butter in a heatproof bowl placed over a saucepan of simmering water. Remove from heat and stir in the vanilla and corn syrup. Whisk in the sugar, a little at a time (at this point the frosting will be quite thick). Place the frosting in the bowl of your food processor and, with the processor running, gradually add the sour cream and hot water. Process until the frosting is nice and shiny. At this point you can simply spread some frosting on the top of each cupcake. However, if you want to pipe the frosting on top of the cupcakes you will have to place the frosting in the fridge for it to firm up. Periodically check and stir the frosting until it is of the desired piping consistency. Garnish each cupcake with shaved or grated white or dark chocolate.

Makes 12 cupcakes