1) Line muffin pans with 12 paper liners. Preheat the oven to 160°C/gas mark 3.
2) Cream the butter and sugar in the bowl of an electric mixer fitted with the paddle attachment until light and fluffy. Add the eggs, 1 at a time. Mix in the chocolate syrup and vanilla. Add the plain flour and mix until just combined. Don't overbeat, or the cupcakes will be tough.
3) Scoop the batter into the muffin cups and bake for 30 minutes, or until just set in the middle. Don't overbake! Let the cupcakes cool thoroughly in the pan.
For the ganache:
Cook the double cream, chocolate chips, and instant coffee in the top of a double boiler over simmering water until smooth and warm, stirring occasionally.