Preheat the oven to 350°F (175°C). Grease a 9×13-inch casserole dish with butter or nonstick spray.

Cut the bread into roughly 1-inch cubes and spread them evenly in the prepared dish.

In a large bowl, whisk the eggs until smooth. Add the milk, heavy cream, sugar, vanilla, and cinnamon, and whisk to combine.

Pour the egg mixture slowly over the bread cubes, pressing the bread down gently so it absorbs the custard. Make sure the custard covers most pieces.

Scatter fresh berries over the top so they sink slightly into the bread.

Cover the dish tightly and refrigerate for at least 2 hours, preferably overnight for maximum flavor and texture.

Uncover and bake on the middle rack for 35–40 minutes. The top should be golden brown and the center set (a knife inserted should come out mostly clean).

Let rest for 5 minutes, then dust with powdered sugar and serve warm with maple syrup.