Take 200g of the butter, hard from the fridge, and cut it into very small pieces. Place the pieces on a tray and leave to soften for 20 minutes.
Put the flour in a bowl, add a few pieces of butter and toss them in the flour using a round bladed knife. Continue adding butter until all of it is well coated in flour, so that no pieces get the chance to clump together. Add the cold water an