Step 1: Prepare the green jelly according to the package instructions and allow it to set completely in a shallow dish, then cut into cubes.
Step 2: Slice your Swiss roll or sponge cake into even rounds, approximately 1.5 to 2 cm thick. Arrange a single layer of these cake slices at the bottom of a large trifle bowl.
Step 3: If using, spread half of the ready-made vanilla custard evenly over the cake layer.
Step 4: Distribute half of the set green jelly cubes over the custard (or directly over the cake if not using custard).
Step 5: In a separate bowl, gently mix the caramel treat with the whipped cream until just combined. Be careful not to overmix. Fold in about half of the crushed Peppermint Crisp chocolate.
Step 6: Spoon half of the caramel and whipped cream mixture over the jelly layer, spreading it gently to cover.
Step 7: Repeat the layers: Add another layer of sponge cake, followed by the remaining custard (if using), the remaining green jelly cubes, and finally the rest of the caramel mixture.
Step 8: Top the trifle generously with the remaining crushed Peppermint Crisp chocolate.
Step 9: Cover the trifle bowl and chill in the refrigerator for at least 4 hours, or preferably overnight, to allow the flavors to meld and the layers to set firmly before serving.