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 cream cheese, 1/2 cup sugar, and vanilla extract until smooth and creamy. Dollop or spread the mixture over the croissants and berries in the dish.
04 - Layer the remaining croissant pieces on top, followed by the remaining blueberries.
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 evenly over the entire casserole. Gently press down on the croissants to help them 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 begins to brown too quickly, cover loosely with foil during the last 10 minutes of baking.
08 - Let the casserole cool for 10 minutes before serving. Dust with powdered sugar if desired. Serve warm.