Preheat the oven to 200ºC / 180ºC Fan / 400ºF / Gas 6. Place the flour, butter and icing sugar in a food processor and mix until fine. With the machine running, pour in about three-quarters of the beaten egg. Open the lid of the food processor and feel the pastry. If you think that it’s moist enough to come together, pulse for another few seconds and turn out onto your countertop. You may well need all of the egg. At the end, the pastry should be neither too firm nor too soft.
Roll out the pastry and line the quiche tin. Place a sheet of baking parchment over the pastry and fill with dried pulses. Bake the pastry in the preheated oven for about 15 minutes, or until it’s just beginning to go golden around the edges. Very carefully remove the dried pulses and the greaseproof paper.