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 of the croissant pieces in the bottom of the prepared dish. Scatter half of the blueberries evenly over the croissants.
03 - In a medium bowl, beat together cream cheese, 1/2 cup sugar, and vanilla extract until smooth and creamy. Dollop spoonfuls of the mixture over the croissants and berries.
04 - Layer the remaining croissant pieces and blueberries on top of the cream cheese mixture.
05 - In a separate bowl, whisk together eggs, whole milk, heavy cream, and 1/3 cup sugar until fully combined and smooth.
06 - Pour the custard mixture evenly over the entire casserole, pressing down gently on the croissants to help them absorb the liquid. Drizzle the melted butter over the top. Let stand for 10 minutes to allow proper soaking.
07 - Bake uncovered for 35–40 minutes until golden brown and set. If the top begins to brown too quickly, cover loosely with aluminum foil during the last 10 minutes of baking.
08 - Remove from oven and let cool for 10 minutes before serving. Dust generously with powdered sugar just before serving.