Pre-heat the oven to 200C/400F/Gas 6. Pour the milk and cream into a pan, add the vanilla pod, and gradually bring to the boil.
Whisk together the eggs, egg yolks and sugar
While the cream is heating, slice the croissants and place in an ovenproof dish, slightly overlapping the pieces. Sprinkle with sultanas and pour over the butter.
Once the cream has boiled, take it off the heat. Add the egg mixture and chocolate and stir well. Set on one side to allow the chocolate to melt, stirring occasionally.
Add the whisky to the cream mixture. Next, using a sieve, strain the cream over the croissants, cover with foil and bake in the oven for 15-20 minutes or until almost set.
Remove from the oven and remove the foil. Coat the top with the jam and serve with ice cream if using.