Pre-heat the oven to 220C/425F/Gas 7.
Heat the cream, milk, vanilla pod and orange in a pan. Bring to a simmer.
Whisk the egg yolks and sugar in a bowl until pale and fluffy. Pour the warm cream mixture over the egg yolks and whisk.
Return to the pan and continue to whisk, to thicken.
Meanwhile, heat the grapes, sugar, butter and orange juice in a pan for 4-5 minutes, stirring occasionally.
Arrange the brioche slices in an ovenproof dish, alternating each layer with the grape mixture.
Pour the custard over and then bake in the oven for 8-10 minutes, or until golden and set.
Remove from the oven and dust with icing sugar, to serve.