Meanwhile make the chocolate decorations, line a tray with baking parchment. Draw pencil shapes on the paper of stars or Christmas trees to use as an outline. Turn the paper over.
Break 50g (2oz) chocolate into a heatproof bowl and melt over a pan of gently simmering water. Ensure the water doesn’t touch the base of the bowl. Remove the bowl from the heat. Spoon the chocolate into a small paper piping bag.
Pipe the outline of the chocolate shapes, using your pencil markings as a guide then pipe lines of chocolate back and forth to fill with a lacy effect. Ensure the chocolate lines are thick enough to prevent the shapes from breaking when they are removed from the tray. Allow to set in a cool place until required.
When the trifle is completely set. Turn out onto a serving platter.
Whisk 200ml (7floz) double cream with 1 tablespoon icing sugar and ½ teaspoon vanilla extract until just standing in soft peaks. Spoon the cream into the piping bag fitted with a star nozzle. Pipe the cream on top of the custard.
Using a small brush dust the chocolate shapes with lustre powder if desired then carefully remove from the parchment and transfer to the trifle to decorate. For extra sparkle flick a little more lustre powder or glitter around the sides and over the top of the triffle. Serve