Take 160 grams of the butter & freeze until completely frozen (this will take at least 2 hours). Keep the remaining butter in the fridge.Make sure to freeze the butter as one large piece - this will make grating it easier. Place the plain flour & salt into a large mixing bowl then mix together.
Cut the refrigerated butter in half lengthways then slice thinly. Add to the mixing bowl & stir so that each individual slice of butter is coated in flour.
Add in enough water to form a rough dough (start with 140g then add in more if required), being careful not to overwork the dough.
Transfer the pastry to a clean work surface & knead until all of the flour has been incorporated. Flatten slightly then wrap tightly in cling film & leave in the fridge for at least 1 hour.
Whilst the dough is chilling, using a box grater, grate the frozen butter into a container then put back in the freezer until needed.
Next, on a lightly floured work surface, roll out the chilled dough into a large 5mm thick rectangle, measuring around 40cm x 25cm.
Dust off any excess flour then sprinkle half of the frozen butter onto the bottom 2 thirds of the dough. Fold the third with no butter on over the middle third then fold the remaining third over the top. Turn the dough 90 degrees clockwise then roll out into a rectangle (again measuring 40cm x 25cm x 0.5cm).Sprinkle the remaining frozen, grated butter over the bottom 2 thirds of dough & repeat the above folding process. Lightly press a finger into one of the pastry's corners to signify how the dough was positioned on the work surface before going in the fridge. Wrap the dough tightly in clingfilm then leave in the fridge for 30 minutes.Make sure to keep a note of which corner you left the indent in. After half an hour, unwrap the dough (save the clingfilm for when the dough goes back in the fridge) & place on the work surface with the indent at the same position as before.
Turn the dough 90 degrees clockwise & repeat the rolling & folding process twice more (this time without adding butter). Remember to turn the dough 90 degrees clockwise before rolling out.Wrap the dough in clingfilm & refrigerate for a further 30 minutes. (Make sure to leave an indent in the same position as before.) Repeat the rolling, folding & turning process twice more for the final two turns then refrigerate for at least 2 hours or preferably overnight before using.