Prepare the bottom and sides of the baking dish with the butter. In a large bowl, add the bread and croissant chunks along with the chocolate chips sprinkled over the top. Toss gently and pour into the prepared dish making sure all the chocolate chips don't settle on the bottom.
In a large bowl whisk together the eggs, brown sugar, cinnamon, nutmeg, milk, chocolate syrup, and 1/2 teaspoon of salt.
Pour the chocolate custard over the bread and chocolate in the dish and press the bread down into the custard to soak it up. Allow to rest for 10 minutes. Then press down a bit again.
Bake uncovered until the edges are golden brown and the center springs back a bit when touched, 45 to 50 minutes. Allow it to cool and settle for about 30 minutes and then make pretty squares, or just dig in right away. Serve with a dollop of Bourbon Whipped Cream, recipe follows. Can also be served cold.
Bourbon Whipped Cream:
In a large bowl whisk the heavy cream until soft peaks form. Add the sugar and bourbon and continue to whisk until stiff peaks form when the whisk is removed from the bowl. Refrigerate and serve cold.