To make the cupcakes: Place the chopped chocolate, cocoa powder and coffee granules/powder (if using) in a medium mixing bowl. Pour the boiling water over and whisk until smooth and all the chocolate has melted. Place in the fridge for 20 minutes.
Meanwhile, preheat oven to 180°C / 160°C Fan / 350°F / Gas Mark 4. Line a 12-hole cupcake/muffin tin with paper cases. In a large mixing bowl, whisk together the flour, sugar, salt and bicarbonate of soda until thoroughly combined. Whisk the oil, eggs, vinegar and vanilla into the now cooled chocolate mixture. Finally, add the wet ingredients to the dry ingredients and whisk until you have a smooth batter.
Divide the batter between the paper cases – I find using an ice cream scoop best for doing this as it makes less mess. Bake for 17-19 minutes or until the cupcakes are well risen and a cake tester comes out clean when inserted into the centre. Leave to cool in the tin for a few minutes and then transport to a wire rack to finish cooling completely.
To make the buttercream: Cream the butter for about a minute or two to soften. Now add the sifted icing in two batches and beat for another 2-3 minutes until the buttercream is light and fluffy. Add the vanilla extract and double cream.
Mix in the melted chocolate until just combined and decorate the cupcakes as desired - I use a large round piping tip to create the ghost shape. Decorate each cupcake with a couple of chocolate chips for the ghosts eyes. The cupcakes will keep in an airtight container at room temperature for up to 3 days.