Preheat oven to 180ºC. In a food processor, or high-powered blender, place raw hazelnuts. Pulse, scraping down sides regularly, until a thick nut butter forms. This can take between 15-25 minutes depending on your appliance. Nuts become a crumb first, and then release their oils to transform into a smooth paste - so be patient!
Add in the sweetener and cocoa powder and process again until combined. If nut butter is too thick, two teaspoons of peanut oil can be blended in to thin it out to a spreadable consistency.
Cut square of defrosted puff pastry in half, into a rectangle. Within each rectangle, cut diagonally from corner to corner, creating two triangles - or four in total for the sheet.
Spoon approximately one tablespoon of nut butter on to the wider end of the triangle and spread upwards for about one third of the pastry. From the larger end, roll pastry up. Bend sides to make a croissant crescent shape.
Place croissants on a baking paper-lined oven tray and brush lightly with beaten egg. Bake for 25 minutes or until golden brown and crispy.
Notes
Experiment with different homemade nut butters: almond and cinnamon, macadamia, honey and cinnamon or chai spiced cashew butter.