Preheat the oven to 200°F to keep the cooked croissants warm as you work in batches.
Prepare the croissants by slicing them in half horizontally, just as you would for a sandwich.
In a large mixing bowl, whisk together the eggs, egg yolks, milk, Grand Marnier (or vanilla), honey, cinnamon, and salt until the mixture is smooth. Pour the mixture into a shallow dish, such as a 9×13-inch casserole dish, for easy dipping.
Heat a large skillet over medium-low heat and melt 2 tablespoons of butter to coat the surface evenly.
Dip the croissants into the egg mixture, ensuring each half is well-soaked on both sides. Let any excess custard drip back into the dish before placing the croissants in the skillet, cut side down.
Cook each croissant for 3 to 4 minutes on the first side, or until golden brown. Flip and cook for another 2 to 3 minutes, ensuring both sides are golden and the custard is cooked through. Adjust the heat if needed to prevent burning.
Transfer the cooked croissants to a baking sheet and place them in the preheated oven to stay warm while you finish the remaining batches.
Once all croissants are ready, arrange them on a serving platter. Garnish with fresh berries, dust with confectioners’ sugar, and drizzle with maple syrup or add a dollop of whipped cream if desired.