A pie stands or falls (literally) on its pastry crust, and this, if I may say so, is a very good one. Actually, it is a Nigel Slater recipe, and I first used it in his Apple Shortcrust Pie. For a 7inch pie dish, you need 100g each of butter and caster sugar, 175g plain flour and an egg yolk mixed with a couple of teaspoons cold water - keep the egg white. I blitz the sugar and butter in a food processor, then add the flour. Pulse until crumbly (you might need to scrape down the sides of the processor) and add the egg yolk and water. Pulse again to mix, tip out onto a sheet of cling film and knead LIGHTLY and briefly into a dough. Flatten, cover and rest in the fridge for at least an hour. Cut in half, roll out one piece into a disc between sheets of clingfilm and line the pie dish. Fill generously with your chosen fruit - in this case, lots of finely sliced rhubarb mixed with sugar and a tablespoon of cornflour - and then top with the remaining pastry, rolled out. Brush the edges with lightly beaten egg white first to seal the two edges. Now brush the surface with more egg white, sprinkle with a teaspoon of granulated sugar, and bake at 170C (fan) for 40 minutes. If it browns too much cover loosely with foil. Simple, crumbly and delicious.