1. Preheat the oven to 180°C/gas mark 4/350°F.
2. Line muffin pans with cupcake liners. I made 15 cupcakes from this mixture but the number of cupcakes will depend on the size of your containers.
3. Put the cocoa, the coffee, if using, and 100g / half cup dark muscovado sugar into a bowl with a bit of space to spare, and pour in the boiling water.
4. Whisk to mix, then set aside.
5. Cream the butter and caster sugar together, beating well until pale and fluffy.
6. While this is going on, stir the flour, baking powder and bicarb together in another bowl, and set aside for a moment.
7. Still mixing, add the vanilla extract into the creamed butter and sugar . Then drop in 1 egg, quickly followed by a scoopful of flour mixture, then the second egg.
8. Keep mixing and incorporate the last of the flour. Then fold in the cocoa mixture, scraping the mixing bowl well with a spatula.
9. Divide this batter into the cupcake liners, filling to just over halfway.
10. Place in the oven and cook until a skewer comes out clean – it was around 18 minutes for me but will depend on the size of your cupcakes.
11. Remove from the tins and cool on a wire rack.

For The Frosting

1. Put the water, 30g / 2 tablespoons muscovado sugar and 175g butter in a pan over a low heat to melt.
2. When this mixture begins to bubble, take the pan off the heat and add the chopped chocolate, swirling the pan so that all the chocolate is hit with heat, then leave for a minute to melt before whisking till smooth and glossy.
3. Leave for about 1 hour, whisking now and again.
4. Spread or pipe the frosting over the cupcakes.
5. Decorate with sprinkles or your decoration of choice.