Preheat the oven to 225 degrees F (110 degrees C). Line a baking sheet with parchment paper and spread out croissant cubes on top.

Bake in the preheated oven until croissant cubes are very dry, 30 to 35 minutes. Turn off the oven and cool cubes slightly.

Lightly spray a 9x13-inch baking dish, add dried croissants, and evenly distribute the blueberries among the croissant cubes.

Whisk eggs together in a large bowl. Add milk, heavy cream, sugar, butter, almond extract, cinnamon, and salt; whisk until well blended. Pour the custard mixture over the croissants, and push croissant cubes down with the palm of your hand or a large spatula to fully submerge. Cover the dish and refrigerate for 2 hours to allow the bread to absorb all of the custard.

Preheat the oven to 350 degrees F (175 degrees C).

Bake in the preheated oven, uncovered, until the top is puffed and golden and the custard is set in the center, 40 to 45 minutes.

Remove the bread pudding to a rack and let cool for 10 minutes.