Cut the sheet of pastry into 3 tall and narrow triangles, like a slice of pizza. Place a tablespoon of the chocolate spread in the base of the triangle then fold over and press to seal with your fingers. Roll the remaining pastry around the pocket of chocolate. Transfer to a baking tray and brush with beaten egg if desired.
Bake in the preheated oven for 8 to 10 minutes, until risen and golden brown. Remove from the oven and serve warm.