Arrange the trifle sponges in a single layer in a glass dish.
Dissolve the coffee in the boiling water, then stir in the alcohol. Pour over the sponges until well soaked.
Whip the cream to fairly stiff peaks, then fold in the custard and vanilla extract if using, and cover the sponges.
Smooth the top and grate over the plain chocolate (or crush in a plastic bag with a rolling pin). Cover and chill for a couple of hours before serving.
This recipe doesn't contain raw eggs (unlike a lot of tiramisu recipes), so it is fine for people with delicate immune systems.
Please note: this recipe has been created and uploaded by a member of the Tesco Real Food online community. Tesco does not test customer recipes so cannot accept responsibility for the content, validate the results or answer queries regarding them.