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 of the blueberries evenly over them.
03 - In a medium bowl, beat together cream cheese, 1/2 cup sugar, and vanilla extract until smooth and creamy. Dollop spoonfuls over the croissant base.
04 - Layer the remaining croissant pieces over the cream cheese, then top with the remaining blueberries.
05 - In a separate bowl, whisk together eggs, whole milk, heavy cream, and 1/3 cup sugar until fully combined and no sugar crystals remain.
06 - Pour the egg mixture evenly over the entire casserole, pressing the croissants down gently to ensure they absorb the liquid. Drizzle melted butter across the top.
07 - Allow the dish to sit at room temperature for 10 minutes so the bread absorbs the custard thoroughly.
08 - Bake uncovered for 35–40 minutes until the top is golden brown and the custard is set. If browning too quickly, cover loosely with foil during the last 10 minutes of baking.
09 - Let the casserole rest for 10 minutes before serving. Dust with powdered sugar if desired and serve warm.