Begin by buttering a 13×9 baking dish.
Spread Nutella on the bottom half of a croissant, then place the top half over it and cut the croissant into slices. Repeat this process for the remaining croissants and arrange them in the baking dish.
In a large mixing bowl, whisk together the eggs, milk, half and half, sugar, vanilla, and salt until well combined.
Pour the egg mixture over the croissants.
Cover the dish and refrigerate it overnight.
Preheat your oven to 350 degrees F.
If you’d like, top the dish with chocolate chunks.
Loosely cover with foil for the first 15 minutes of baking, then remove the foil and bake for an additional 20-30 minutes.