Whip the cold full cream with about 4 tablespoons of fine or castor sugar. Using a stand mixer, until forms peaks. Put aside, in fridge covered.
Once the cake is cooled, cut into squares needed. Place some in the bottom of a large glass trifle bowl. Keep enough sponge cake for three layers. Drizzle some cherry liquid to the cake pieces. (if you want to use cherry liqueur you may.)
Add some chocolate custard mixture. Remember you are making layers so keep for at least for three layers.
Then add some cherries as another layer and make sure they show separately on the side of the glass bowl.
Then start and make the next two layers the same, ending with a topping of whipped cream, decorate with cherries in the middle and some fresh glazed whole cherries standing up and grated chocolate for decoration on the whipped cream. (or use some cocoa powder)
Keep in the fridge covered until served for a dessert. You can make this trifle a day ahead.
Serve for a dessert on Christmas day after a meal. Your family will enjoy it.