01 - Preheat oven to 350°F. Grease a 9x13-inch baking dish thoroughly 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 extract until smooth and creamy using an electric mixer or whisk.
04 - Dollop or spread the cream cheese mixture over the croissants and berries in the dish.
05 - Layer the remaining croissant pieces and blueberries on top of the cream cheese layer.
06 - In a separate bowl, whisk together eggs, whole milk, heavy cream, and 1/3 cup sugar until well combined and smooth.
07 - Pour the custard mixture evenly over the entire casserole. Press the croissants gently with a spatula to ensure they absorb the liquid.
08 - Drizzle melted butter over the top. Let stand for 10 minutes at room temperature to allow the croissants to fully soak.
09 - Bake uncovered for 35–40 minutes until golden brown and set. If the top browns too quickly, cover loosely with aluminum foil during the last 10 minutes of baking.
10 - Let cool for 10 minutes before dusting generously with powdered sugar. Serve warm.