Preheat your oven to 350°F (175°C) and grease a 9x13 inch baking dish with unsalted butter.

Combine whole milk, heavy cream, and butter in a medium saucepan over medium heat. Stir until the butter melts and mixture is hot but not boiling.

Remove saucepan from heat and add finely chopped dark chocolate, stirring until it melts completely and becomes smooth.

In a separate mixing bowl, whisk together eggs, granulated sugar, vanilla extract, and a pinch of salt until fully combined.

Gradually pour the warm chocolate mixture into the egg mixture, whisking vigorously to prevent the eggs from scrambling.

Fold in the day-old bread cubes gently, ensuring each piece is well coated. Let sit for about 10 minutes.

Transfer the bread pudding mixture into the prepared baking dish, spreading evenly. Bake for 50 minutes until puffed and lightly golden.

Let the pudding cool for at least 30 minutes before slicing. Serve with vanilla ice cream or a drizzle of caramel sauce.