01 - Preheat oven to 350°F and line a baking sheet with parchment paper.
02 - Grind pistachios finely in a food processor. Add softened butter and powdered sugar; blend until creamy. Incorporate the egg, vanilla extract, flour, and salt; process until smooth and fully combined.
03 - Cut each croissant horizontally while keeping the back edge intact to form a hinge.
04 - Brush the inside of each croissant with simple syrup if using to enhance moisture retention.
05 - Spread a generous layer of pistachio cream inside each croissant, close the hinge, and arrange on the prepared baking sheet.
06 - Coat the exterior of each croissant with a thin layer of pistachio cream and sprinkle generously with chopped pistachios.
07 - Bake for 15-20 minutes until the surface turns golden brown and the filling sets.
08 - Allow to cool for a few minutes, then dust generously with powdered sugar before serving warm.