• Preheat the oven to 375°F. Liberally butter the baking dish.

Prepare Croissants

• Cut the croissants in half, laterally, so you have a top half and a bottom half. Lay the croissants open, cut side up. This will help to dry the interior of the croissant. Stale bread soaks up the custard and holds its structure so the croissant bake isn't soggy.

Mix the Custard

• Using a Microplane or a box grater, zest the lemons. You should have approximately 1 tablespoon of zest.
• Juice the lemons. You should have approximately ⅓ cup of juice.
• Crack 6 eggs in a medium bowl. Whisk until the yolks and whites are thoroughly combined. Add the buttermilk.
• Whisk in the lemon zest, juice, and the vanilla extract.

Assemble the Bake

• Lay the croissant halves on a slant in the prepared baking dish.
• Randomly lay the blueberries between the layers of croissants and along the sides. Be generous - the juicy blueberries will become syrupy in the egg mixture.
• Pour the custard over the croissants, making sure to get some in between the layers.
• Press the croissants into the egg mixture and allow them to soak for 15 minutes.

Baking Instructions

• Coat a sheet of aluminum foil with cooking spray. Cover the croissant bake with the foil.
• Place the baking dish in the preheated oven. Bake for 25 minutes.
• Take the dish out of the oven and remove the foil. Place the croissant bake back in the oven to crisp the top.
• Bake for 10-12 minutes.
• To check the doneness of the casserole, insert a toothpick in the center. If it comes out clean, the baking is done. The internal temperature should be at least 165 degrees.