To make the rich shortcrust pastry, whizz the flour and butter to breadcrumbs in a food processor. Add the egg yolks and pulse until it starts to come together (you might need to add a splash of cold water). Wrap in clingfilm and chill for 30 minutes. Heat the oven to 190c/fan 170c/gas 5. Roll the pastry out on a lightly floured surface then line a 24cm × 4cm tart tin. A good chef’s trick is to leave the excess pastry draped over the edges of the tin to stop it from shrinking. Line with baking paper and beans then put on a baking sheet and bake for 15 minutes. Take out the beans and paper, brush all over with egg white (left from the pastry) and bake for another 10 minutes. The egg white will seal any cracks in the pastry and stop it going soggy. Take out of the oven to cool, and turn the oven down to 180c/fan 160c/gas 4.