Place flour, icing sugar, butter and a pinch of salt in the food processor. Blitz until the mixture resembles coarse breadcrumbs.
With the machine running, add egg yolk, then iced water. Continue to process until mixture just comes together to form a ball. Remove from processor, knead briefly on a floured surface, then roll the dough into a flat disc. Wrap in cling film and refrigerate for 30 minutes.
Grease a 23cm flan tin and line the base with baking paper.
Remove chilled pastry from fridge and roll out on a lightly floured surface to a thickness of about 3mm. Carefully lift the pastry with a rolling pin and press it into the flan tin. Return to fridge and refrigerate for 30 minutes.
Heat oven to 180°c. Remove flan tin from fridge and prick the base with a fork all over. Place a piece of crumpled baking paper in the flan shell, and fill with baking weights or uncooked beans or rice.
Bake blind for 20 minutes.
Remove the baking weights and paper, and continue to bake for a further 10 to 15 minutes, until crust is just golden. Watch it very closely in the last few minutes!
Leave the flan crust in its tin, and cool on a rack until completely cold.