Please do use stale croissants for this - the grocery store variety are perfectly fine. They lend a lightness that breads, even rich ones like brioche, just don't have. No bourbon? Use brandy instead. Even cognac. —boulangere
stale croissants (grocery store variety are just fine)
Split the croissants through the middle lengthwise, then cut into 1" cubes and transfer to a large mixing bowl.
Crack the eggs into a bowl and whisk them together. Add the sugar in a steady stream, whisking all the while. Add the vanilla extract, bourbon, heavy cream, and spices. Whisk to blend.
Pour the cream mixture over the croissant cubes. Using a spatula, fold gently to blend. Let sit for 5 minutes so the croissant cubes can absorb some, but not all, of the liquid.
Fill 8-ounce ramekins to within 1/2" of top. Set them in a 9"x13" baking pan. Set the pan in the oven, just hanging slightly over the front edge of the rack. Fill the baking pan halfway with very hot tap water. Gently slide the pan the rest of the way into the oven.
Bake until custards are puffed and nicely browned, about 20-25 minutes. Carefully remove baking pan from oven. Lift ramekins from baking pan (I use a canning jar lifter for this step) and allow to cool before refrigerating or serving.
To serve, bring to room temperature. Perhaps drop a scoop of ice cream on top along with a few gratings of fresh nutmeg.