Chill four dessert plates in the fridge.
Put the egg yolks in a small bowl and whisk in the sugar to make a paste.
Next, pour the milk into a small pan.
If using the vanilla pod, add it to the milk and slowly heat on the lowest setting for 10 minutes, without boiling. Then remove the vanilla pod.
If using vanilla extract, omit heating the milk for 10 minutes first but add it to the cold milk now.
Bring the milk up to the boil.
Now slowly stir the milk and vanilla into the egg and sugar until the mixture is smooth.
Return the custard to the pan and stir, over a low heat, until it begins to thicken. You want it to thicken enough to be able to coat the back of a spoon. Do not let it boil. Remove from the heat and pour into a bowl. Cover the custard with cling film/plastic wrap to prevent it forming a skin and then leave it to cool.
Meanwhile, cut each sponge finger in half to give two small fingers and lay them in a shallow bowl. Drizzle over the wine or sherry.
Next, wash and pat dry the fruits. Remove the currants from their stalks and hull and halve the strawberries.
Set aside half the berries and currants, picking out the best ones.
Put the remainder in a food processor or blender and add the wine and sugar.
Purée until smooth and then, using the back of a spoon, push through a plastic sieve to remove the pulp. Once the purée is pressed through, wipe the underside of the sieve with a clean spoon to get all the sauce.
Roughly chop the pistachio nuts or walnuts.
Whip the cream until it forms soft peaks.
Stir one spoonful into the cooled custard to loosen it a little and then fold in the remaining cream.
Now to assemble, carefully toss the reserved fruit with half the purée and spoon into the centre of each cooled plate.
Arrange the sponge fingers evenly around the edge of the plates.
Pour the custard over half of each the sponge finger then sprinkle the nuts on top of the custard.
Pour the remaining purée over the fruit and serve.