You can speed this recipe up further by using a pouch of bought creme patissiere from the baking aisle - they usually do chocolate although you might not find coffee flavour.
Melt 80g of the dark chocolate in the microwave retaining a few squares to grate over afterwards.
Spread 1 tablespoon of the dark chocolate over each tart case, smooth over the surface to the edges.
Put the chocolate covered cases in the fridge for ten minutes to help them set.
Remove the cases from the fridge and spoon over 1 generous table spoon of creme patissiere and swirl round with a spoon to look even.
Grate over the remaining dark chocolate. You can serve them immediately but they're best chilled for an hour to be eaten nice and cold. They'll keep in the fridge for 3 days.