Roll out the pastry on a lightly floured work surface to a rectangle measuring 25 x 35cm (10 x 13¾in).
Using the diagram as a guide, lightly mark your triangles in the dough surface with a knife.
Once you are happy with the position of your triangles, cut the dough using a pizza wheel. You should have 5 triangles plus two half-triangles from the ends. Take the two triangular off cuts at either end and stack them one on top of the other. Roll with the pin to secure them together and gently encourage into a piece big enough to cut out the remaining croissant triangle.
Take one triangle at a time and place it with the pointed end facing you. Gently tug the top corners outwards and then roll the triangle up loosely. The thin point should fold over the top and touch the surface but not sit underneath.
Transfer the croissants to a well greased baking sheet, cover and allow to rest for 10 minutes. After resting, gently curve the croissants into a crescent shape. Cover again and leave to rise for 2 hours or until nearly doubled in size.
Once they are risen, chill them for 30 minutes. Brush them well with beaten egg and bake in the preheated oven for 15–18 minutes until they are a deep golden brown. Serve warm.