In a stand mixer bowl, place the flour, salt and water (at room temperature). Mix with a dough hook at medium speed for a few minutes. Transfer the dough to a worktop and shape it into a compact ball (a détrempe). Score the top of the ball with a cross, wrap in cling film and refrigerate (minimum 30 mins).
With your fingers, squash the four corners of the ball. Roll out the ball, maintaining the ‘cross’ shape. The centre should be thicker. In the centre, place the butter (room temperature). Shape butter into a rectangle that fits in the centre of the dough. Fold the top corner of the dough over the butter. Fold the opposite side (bottom) over. Fold the right corner over making sure the edges are sealed and regular. Brush off excess flour every time. Fold the left corner over. With the butter completely enclosed, bash the square with a rolling pin to incorporate the butter into the dough. Make sure the square shape is maintained. Roll out the square lengthwise making sure the butter is not coming out of the dough. Shape the dough into a long rectangle, to a thickness of about 1cm. Give the dough a quarter-turn anti-clockwise. Flatten the corners if necessary. Fold the dough into three parts. Start by folding the right third over, then the left third (making sure the edges are sealed and regular). Roll out the pastry again, lengthwise. Give the dough a quarter-turn (anti-clockwise) and fold into thirds again. Start by folding the right third over, then the left one. Make sure the edges are sealed and regular. Make a mark in the dough by sticking 2 fingers in (it means the dough has been folded twice).
Wrap dough in cling film and refrigerate for at least 30 mins. The first two folds are done. When it has been folded 4 times, stick 4 fingers in it; when folded 6 times, stick 6 fingers in it. Puff pastry needs to be folded 6 times, twice at a time followed by the chef’s ‘finger mark’ and 30 mins in the fridge (wrapped in cling film). When making the subsequent quarter turns it must always be in the same direction (in our case anti-clockwise). When the pastry has been folded 6 times (and bears 6 finger marks) it is ready to use (after 30 mins wrapped in cling film in the fridge. Puff pastry can be stored for up to 4 days in the fridge, and for several weeks in the freezer (wrap in cling film for optimal storage conditions).