Prepare the jelly according to packet instructions, but do not place it into the fridge to set.
Cut the Swiss roll into 12 equal slices and arrange them over the base and a short way up the sides of a glass trifle bowl. Put any remaining slices in the middle of the bowl.
Spoon the sherry over the Swiss roll slices and allow to soak into the sponge for a few minutes. Scatter the fruit on top of the soaked sponge. Pour the prepared jelly over the fruit. Cover the dish with cling film and leave to set in the fridge for about two hours.
Meanwhile, for the custard, pour the milk and cream into a medium heavy-based pan. Add the vanilla pod and seeds, then slowly bring to the boil. Once the mixture comes to the boil, remove from the heat and set aside to infuse for 15 minutes. Remove and discard the vanilla pod.
Mix the cornflour with the water in a small bowl until smooth and well combined, then set aside.
Whisk the egg yolks and sugar in a large bowl until pale and fluffy. Gradually stir the warm milk and cream mixture into the egg and sugar mixture until smooth. Return the mixture to the saucepan and heat over a low heat.
Cook for around 8-10 minutes, stirring continuously, until the custard has thickened enough to coat the back of a wooden spoon.
Give the cornflour mixture a stir, then mix quickly into the custard. Cook for 1-2 minutes more, or until the custard is very thick and smooth, stirring continuously.
Remove the pan from the heat and pour the custard into a bowl placed over a second bowl filled with iced water. Cover the surface of the custard with cling film to prevent a skin from forming. Set aside until the custard has cooled.
When the custard has cooled, remove and discard the cling film. Stir the custard a few times, then gently pour onto the set jelly.
Cover with cling film and return the trifle dish to the fridge for a further 30 minutes, or until the custard is lightly set.
For the topping, lightly toast the almonds in a dry frying pan over a low heat for 2-3 minutes, or until golden-brown (keep the almonds moving around the pan frequently to prevent them from burning). Set aside to cool.
Whip the cream in a bowl until soft peaks form when the whisk is removed. Spoon the whipped cream over the custard, starting at the sides of the bowl before working your way into the middle. Scatter over the almonds, cover and return to the fridge until ready to serve.
To serve, spoon the trifle into serving bowls and eat immediately.