Put the plums in a saucepan with the conserve and 600ml of water. Bring to the boil, then simmer gently for about 10 minutes until the plums are very tender.
Empty the jelly sachet into a medium bowl and pour on the hot plum mixture. Stir well until the powder has dissolved through the plums.
Dip the madeleines quickly into whatever alcohol you’re using. Cut about 2cms from the base of each one and press the larger pieces around the edge of your trifle dish. Cover the base of the dish with the smaller cut pieces. Drizzle over any remaining alcohol.
Spoon on the plum mixture, allow to cool then chill to set.
Spoon the vanilla custard over the set plum jelly.
Finally, whip the cream until it just holds its shape in soft peaks. Spoon on top of the custard. Sprinkle with chopped toffees or fudge sweets.
Make the trifle a day ahead and keep covered in the ‘fridge, without the cream. About an hour before serving, add the whipped cream and decoration and keep in the ‘fridge.
Sachets of fruit flavoured jelly powder are available in most supermarkets.
