Preheat the oven to 350F and line a baking sheet with parchment paper or a nonstick baking mat.
Using a bread knife, making a horizontal slice but leave a little connection on one side of the croissant. Open the croissant up like a book.
Scoop a generous amount of the pistachio cream filling into the croissant and close the croissant. Spread a little more cream on top of the croissant and sprinkle with the chopped roasted pistachios.
Bake in the oven for 15-20 minutes, until the pistachio cream is slightly golden brown. Let cool and sprinkle with powdered sugar to taste and enjoy.
If you have leftovers, store in the refrigerator and pop the croissants back into the oven to re-heat before enjoying again.