Preheat the oven to 220C/425F/Gas 7.
Place the cream, milk, chocolate and whisky in a pan and heat until the chocolate has melted. Stir gently to combine.
Place the eggs, egg yolk and sugar in a bowl and whisk until pale and fluffy.
Pouring gradually while whisking, add the hot chocolate milk mixture to the whisked eggs.
Transfer the chocolate milk and eggs mixture back to the pan. Heat gently, whisking constantly, until the custard has thickened.
Arrange the bread slices in an ovenproof dish and pour the chocolate custard evenly over. Allow to sit for a few minutes to absorb, then place in the oven to bake for 10-12 minutes, or until set.
Remove from the oven and serve.