The night before place the prunes in a saucepan with 75ml of water, simmer for 15 minutes then leave to cool.
Drain the cooled prunes, discard the liquid, then put the soaked prunes in a bowl with the Armagnac, cover and leave overnight.
To make the batter sift the flour and salt into a large bowl, now make a well in the centre of the flour.
Then whisk the yolks and milk together and pour about 4 tablespoons of this in the centre of the well and begin to whisk gradually incorporating the flour from around the edge of the bowl.
As you whisk continue adding small quantities of the milk mixture until it’s all been added.
Then use a rubber spatula to scrape any elusive bits of flour from around the edge into the centre, add the vanilla and 1 tablespoon of the sugar then whisk once more until the batter is smooth.
Pre-heat the oven to 180°C, gas mark 4.
Now cut the prunes in half and tip them plus their juice into a medium sized bowl. Then peel, core the apples and cut them into smallish chunks (about 1cm) and add them to the prunes and give them a stir to coat them in the Armagnac juices.
Next whisk the egg whites to the soft peak stage, then carefully fold them into the batter using a large metal spoon.
Pour the batter into the pan then sprinkle the prunes and apples evenly over the top followed by the remaining sugar.
Bake in the centre of the oven for 35 - 40 minutes until well-risen and golden brown.
Rest for 10 minutes then to serve, loosen all round the edge with a palette knife then cut into 4 or 6 and use a fish slice to serve either warm (or cold) with a dusting of icing sugar and some chilled Jersey cream or crème fraîche