Preheat the oven to 350ºF. Spray a 9x13-inch baking dish with nonstick cooking spray.

Cut the bread into 1 inch cubes. If the bread is stale, add it to the prepared baking dish. If it is more fresh, spread it out in a single layer on a baking sheet. Bake in the oven for 10 minutes, mixing halfway though the baking time. Then transfer the bread cubes to the baking dish.

Combine the milk and the cream in a small saucepan and heat over medium heat until right before it starts to boil.

While the milk is heating, combine the eggs, egg yolks, and sugar and whisk until smooth. Slowly whisk in the hot milk mixture, making sure to vigorously whisk as you are adding it to avoid curdling the eggs. Add all of the bittersweet chocolate and half of the semi-sweet chocolate. Continue to whisk until the chocolate is melted.

Pour the chocolate custard over the top of the bread in the baking dish. Use your hands or a spatula to gently press the bread down into the custard, making sure all of the bread is soaked.

Sprinkle the remaining semi-sweet chocolate evenly over the top. If desired, use your hands or a spatula to gently press the chocolate in so that not all of it is on top of the bread.

Transfer the dish to the oven. Bake until the pudding is puffed and browned, 35-45 minutes. If you shake the dish, it will have just a slight jiggle to it. Remove from the oven and let it sit for 5-10 minutes.

Serve the bread pudding warm or at room temperature, topped with fresh whipped cream, if desired.