Butter two small gratin dishes and distribute the chopped brioche into the base of each.
Whisk the custard, egg yolk, cream, and Sauternes in a saucepan over heat until warm.
Pour half of the warm custard mixture over the brioche pieces.
Melt the butter in a pan and fry half of the chopped apple until caramelised.
Top the dishes with the caramelised apple and pour over the remaining custard.
Cover the dishes with cling film and microwave on high for four minutes.
Let the puddings rest for two minutes while preparing the garnish.
Slice the remaining apple into rings and place on a baking sheet with icing sugar.
Caramelise the apple rings using a blowtorch or grill.
Garnish each dish with the caramelised rings and serve immediately.