Prepare the Croissant Casserole: Butter a 9 x 13-inch (3-quart) baking dish; place on a rimmed baking sheet.
Whisk cream cheese, powdered sugar, and 1/4 teaspoon of the vanilla together in a medium bowl until smooth and well combined. Set aside.
Whisk eggs, milk, granulated sugar, butter, lemon zest, cardamom, salt, and remaining 2 teaspoons vanilla together in a large bowl until well combined.
Halve 12 of the mini croissants (or 6 large) crosswise using a serrated knife; reserve top halves. Cut bottom halves and remaining 12 mini croissants (or 6 large) into 1- to 2-inch pieces (about 12 cups).
Arrange two-thirds (about 8 cups) of the cut croissant pieces in an even layer in prepared baking dish. Dollop cream cheese mixture and lemon curd over croissant pieces as desired. Top evenly with remaining croissant pieces (it’s OK if some cream cheese mixture and lemon curd peeks through); pour about half of egg mixture evenly over top.
Dip reserved croissant tops in remaining egg mixture just until saturated; arrange and gently press, cut sides down, in an even layer over top. Pour any remaining egg mixture over top. Cover with aluminum foil and let stand at room temperature 1 hour.
Meanwhile, preheat oven to 350°F. Prepare the Macerated Berries: Add 1/2 cup of the blueberries and 1/2 cup of the blackberries to a medium bowl; thoroughly mash using a potato masher or fork. Stir in sugar, lemon juice, remaining blueberries, and remaining blackberries until combined. Let stand at room temperature, stirring occasionally for at least 1 hour or until Croissant Casserole is ready to serve.
Bake Croissant Casserole, covered, in preheated oven for 45 minutes; uncover and bake until golden brown, set, and cooked through, 15 to 30 minutes more. Dust top with confectioners’ sugar; top with some Macerated Berries. Serve immediately with any extra Macerated Berries.
