Preheat the oven to 350°F (175°C).

Cut croissants into bite-sized pieces and place in a greased baking dish.

In a mixing bowl, whisk together eggs, milk, heavy cream, granulated sugar, vanilla extract, and cinnamon (if using).

Pour the egg mixture over the croissants, ensuring all pieces are well coated.

Sprinkle mixed berries over the top of the croissant and custard mixture.

Bake in the preheated oven for 30 minutes or until golden and set.

Let cool slightly before dusting with powdered sugar and serving.