To make the dough mix together the strong white flour, salt, caster sugar, dried yeast and warm water. Knead it for 10 minutes, then put it into a bowl covered with cling film and chill it in the fridge for 1 hour
Bash up and flatten the butter between two sheets of greaseproof paper using a rolling pin
Roll out the pastry into a long rectangle and place the flattened butter in the middle
Fold the pastry around the butter like an envelope, wrap it in cling film and chill in the fridge for 1 hour. Do this twice more, then leave in the fridge overnight
The next day, pre-heat your oven to 220C/425F/Gas Mark 7
Cut the dough in half. Roll out the first half of the dough into a long rectangle. Cut it into three squares, then each square into triangles making 6 triangles. Do the same with the second half of dough
Roll up the triangles and lay onto a lined baking tray
Brush them with beaten egg, then bake for 10 minutes, then turn the oven down to 190C/375F/Gas Mark 5 and bake for a further 5 minutes