01 - Preheat oven to 350°F. Grease a 9x13-inch baking dish with butter or cooking spray.
02 - Slice croissants into 1–2 inch pieces. Arrange half the pieces in the bottom of the prepared dish and scatter half the blueberries evenly over them.
03 - In a medium bowl, beat together cream cheese, 1/2 cup sugar, and vanilla extract until completely smooth and creamy.
04 - Dollop or spread the cream cheese mixture over the croissants and berries in the baking dish.
05 - Layer the remaining croissant pieces on top, then scatter the remaining blueberries over the surface.
06 - In a separate bowl, whisk together eggs, whole milk, heavy cream, and 1/3 cup sugar until completely combined and smooth.
07 - Pour the custard mixture evenly over the entire casserole. Gently press down on the croissants to help them absorb the liquid.
08 - Drizzle the melted butter evenly over the top. Let stand for 10 minutes to allow the croissants to soak up the custard.
09 - Bake uncovered for 35–40 minutes until golden brown and set. If the top browns too quickly, cover loosely with foil during the last 10 minutes.
10 - Let the casserole cool for 10 minutes before dusting with powdered sugar and serving warm.