Place raisins in a small bowl. Pour rum over fruit and set aside at room temperature for several hours or overnight. Drain raisins,reserving rum.

Preheat oven to 150°C. Grease an ovenproof dish – square or round – at least 5cm deep and about 25cm across.

Place a layer of croissant pieces in base,sprinkle with raisins and chocolate and add another layer of croissant,then raisins and chocolate and so on. Reserve a handful of raisins and chocolate to sprinkle on top.

Bring milk,cream,salt,vanilla beans and reserved rum to the boil in a saucepan. Remove from heat and discard vanilla beans. Set aside.

In a large bowl,whisk eggs and sugar together,then slowly pour in milk mixture,whisking constantly. Carefully pour custard over croissant layers,sprinkle with reserved raisins and chocolate and bake for 1 hour,or until custard is just set.

Dust with icing sugar and serve with double cream or ice-cream.