Puff pastry has a reputation as being difficult to make. It really isn't hard, but it is a bit laborious. However, this rough puff is far better than any shop-bought pastry - lusciously buttery and crisp, cheaper than shop-bought and nowhere near as hard to make as you think..
If your kitchen is warm, chill the flour, water and butter in the freezer for 10 minutes before you start. Cut the butter into small dice - about 1cm (half an inch). Stir the salt into the flour, then add the cubes of butter, making sure they are not sticking together. Stir the butter around and get each piece coated in flour. Add the water, and stir until you have a thick dough.
Tip the mixture out onto a floured worktop and roll it out into a long rectangle that is about three times longer than it is wide. Using a pastry scraper or ruler, straighten the edges and then fold the pastry into thirds, so you have a more or less square chunk. Using your rolling pin, flatten the three open edges, then rotate the chunk through 90 degrees. Roll it out into a long rectangle again and repeat the process of straightening the edges, folding into thirds, pressing down the edges and rotating the block. You'll need to do this 5 or 6 times until you have a smooth sheet of pastry.
Finally, fold the pastry into thirds again and tidy up the edges. You can use the pastry after it has rested in the fridge for about half an hour, or you can keep it in the fridge for a few days before you're ready to use it. Alternatively, this pastry freezes very well and can be kept frozen for up to three months.