Preheat oven to 350 degrees Fahrenheit (175 degrees Celsius) and grease a 9x13 inch baking dish.
Spread the croissant pieces evenly in the baking dish and sprinkle chocolate chunks throughout the layers.
Whisk eggs, milk, heavy cream, sugar, vanilla, cinnamon, and salt in a bowl until fully combined.
Pour the custard mixture over the croissants and press down lightly to ensure absorption.
Allow the mixture to rest for 15 minutes at room temperature.
Bake for 40 minutes or until the custard is set and the croissant tops are golden and crisp.
Let cool for 5 minutes before serving.