To make the pastry, add the flour, icing sugar and salt to a food processor, and pulse briefly to mix. Add the butter and pulse briefly, a dozen or so times, until you have coarse crumbs, resisting the temptation to over-process or the pastry can become tough rather than tender. Add ice-cold water 1 tsp at a time, pulsing briefly between additions, until the mixture starts to just clump together. Tip onto a sheet of clingfilm and wrap into a ball, just pressing gently together, no need to squeeze hard or knead, tiny air gaps are a good thing with pastry. Chill in the fridge for 30 minutes.