Whisk the eggs, 1/4 cup sugar, the milk, orange zest, orange juice and vanilla in a large bowl.

Put the croissants in and 8-inch square baking dish, squeezing them in to fit in a single layer.

Pour the egg mixture over the croissants, then put a plate on top and press down to keep submerged.

Let soak in refrigerator, at least 30 minutes upto an hour.

Preheat the over to 350°F. Remove the plate from croissants, cover the baking dish with aluminum foil and bake until set, about 40 minutes.

Remove from the oven and turn on the broiler. Uncover the baking dish, sprinkle with remaining 1 tbsp sugar and broil until sugar is bubbling in spots, about 2 minutes.

Meanwhile, mix the marmalade with 1/4 cup water in a small microwave-safe bowl; microwave until warm, 1-2 minutes. Serve on the side.