Stir in the vanilla and cinnamon. Pour over the bagel pieces, cover, and refrigerate for at least two hours or up to overnight. The longer it soaks, the more of the custard will be absorbed.
Slices of bread are soaked throughly in beaten eggs. If serving as a sweet dish, milk, sugar, vanilla or cinnamon can be added to the eggs or if serving as a savoury dish, season with salt and pepper.
Try out your own experimental toppings and use the recipe in Food & Wine's guide as a starting point. There's no end to the way you can flavor your French toast.