Preheat the oven to 350°F. Grease a 9x13 inch baking dish with butter. Set aside.
Tear the croissants by hand and add as many as needed to completely fill the baking dish with no spaces between the croissant pieces. (This number will vary depending on the size of thee croissants.) Scatter the fresh blueberries over the top.
6-8 croissants, 1 cup fresh blueberries
In a large mixing bowl, combine the eggs, milk, heavy cream, sugar, vanilla, cinnamon and salt. Whisk together until completely combined.
4 large eggs, 1 ½ cups milk, ½ cup heavy cream, ½ cup granulated sugar, 1 tablespoon vanilla extract, ½ teaspoon ground cinnamon, ¼ teaspoon fine sea salt
Pour the custard over the croissants. Let it sit for 15 minutes which will give the croissants time to soak up some of the custard. Alternatively, cover with plastic wrap and put in the fridge overnight.
Cover the dish with foil and bake for 25 minutes (removing plastic wrap first if refrigerated overnight). Remove the foil and bake for an additional 15 minutes or until golden brown and the custard has set.
Once baked, dot spoonfuls of the mascarpone between the croissants, spoon wild blueberries as desired and drizzle over the maple syrup. Dust over some powdered sugar if you wish.
½ cup mascarpone, ¾ cup wild blueberries, ½ cup maple syrup, powdered sugar
Serve while still warm from the oven. Enjoy!