Leftover brioche, challah work in this recipe but nothing beats it when made with big, puffy croissants (even slightly stale ones will work).I love the Costco KIrkland croissants for this actually. This dish has an overnight rest in the fridge. It is a vanilla-tinged egg custard bath, which soaks the coisrsants. Next day, just bake and watch it puff up in the oven. Serve hot with warmed maple syrup nearby. Crumbled maple sugar would be nice to finish this off, but a dusting of cinnamon and icing sugar is fine.