Preheat the oven to 325 degrees F. Butter or use nonstick spray on a 13 by 9-inch baking dish.
Spread the bread cubes in the prepared dish. Place the grated chocolate in a medium bowl; set aside.
In a large bowl, whisk together the sugars, cocoa powder, and cinnamon. Whisk in the eggs, 1 at a time. Stir in the vanilla.
In a medium saucepan, bring the milk and 1/4 cup cream to a boil. Pour the mixture over the grated chocolate and stir until the chocolate is completely melted. Whisking constantly, slowly pour the chocolate mixture into the egg mixture. Stir in the bourbon and pour the chocolate mixture evenly over the bread cubes. Refrigerate pudding for at least 1 hour or up to 12 hours.
Bake the pudding until just set and a knife inserted in the center of the pudding comes out clean, about 1 hour. Serve the pudding warm or chilled with Chocolate Whipped Topping.
Chocolate Whipped Topping:
Beat together the sugar and 1 cup cream. Once soft peaks form, fold in the chocolate sauce.