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 in the bottom of the prepared dish. Scatter half of the blueberries evenly on top.
03 - In a medium bowl, beat together cream cheese, 1/2 cup sugar, and vanilla until smooth and creamy. Dollop or spread over the croissants and berries.
04 - Layer the remaining croissants and blueberries on top of the cream cheese mixture.
05 - In a separate bowl, whisk together eggs, milk, heavy cream, and 1/3 cup sugar until well combined and sugar is dissolved.
06 - Pour custard evenly over the casserole, pressing the croissants gently to ensure they absorb the liquid. Drizzle melted butter over the top. Let stand for 10 minutes.
07 - 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.
08 - Let cool for 10 minutes before dusting with powdered sugar and serving warm.