- Slice and cube brioche and place in large bowl. Butter an 11×14-inch baking pan. Set aside.
- In very large bowl, whisk together yolks, sugar, cinnamon, salt, and vanilla until smooth.
- Whisk in cocoa powder and whole milk. Add heavy cream and stir until thoroughly blended.
- Pour chocolate mixture over brioche, being sure to cover all cubes. Cover with plastic wrap and refrigerate for 2 hours.
- Preheat oven to 375 degrees. Remove bread mixture from refrigerator and stir in chocolate chips. Pour into prepared pan and cover with foil.
- Bake for 30 minutes. Remove foil and bake for 15 minutes more. Use toothpick to check if pudding is cooked through: Toothpick will come out clean, unless you stab a chocolate chip. Allow to rest for 15 minutes.
- To make sauce, heat whiskey and sugar in small saucepan over medium heat until sugar is completely dissolved. Turn heat to low, add heavy cream and let simmer until ready to serve.
- Slice bread pudding as desired and finish with whiskey cream sauce.