Put the port, wine, 100ml water, lemon rind, sugar, star anise and cinnamon stick into a saucepan large enough to hold the quartered pears in a single layer. Bring to the boil, turn down the heat and simmer for five minutes.
Add the pears and poach until they are tender – this can take anything from 15 to 30 minutes, depending on their ripeness – turning them over periodically. Test with a fine skewer to check whether they are cooked. If you can leave them soaking in the liquid overnight, they’ll darken and become even more fragrant. Remove the pears with a slotted spoon and put them into a bowl. Discard the spices.
Make the cranberry mixture, allowing yourself plenty of time for it to cool. Put the fresh and dried cranberries into a medium saucepan with the poaching liquor from the pears and bring to the boil.
Turn down the heat and simmer for about six minutes. The liquid should be thick and syrupy, and about two-thirds of the cranberries will have popped. Leave to cool completely. You will end up with a rough purée.
Cut the sponge cake into slices. Layer everything in a glass serving-bowl, soaking well in port as you go, starting with half of the sponge slices, then half of the pears, half the cranberry purée and half the custard. Repeat so that you have two layers of each. Cover with clingfilm and, if you wish, chill until the next day.
Bring the port and dried cranberries to the boil, and immediately take off the heat. Leave to soak for 30 minutes, or until completely cool. Drain. Just before serving, whip the cream, and add the vanilla and icing sugar to taste. Spread this over the top of the trifle and sprinkle on the nuts and the soaked cranberries.