Using a pastry cutter or food processor, mix together the flour, sugar, salt and butter, until the butter is cut into very small pieces. Add the egg yolk and vanilla, and mix by hand until the pastry starts to form up. Place the dough into a 10" tart tin with a loose base, pressing into the tin until a crust has been formed, and poke holes with a toothpick or skewer. Place in the fridge for an hour. Place pie weights onto the crust, and bake at 375ºF/190ºC for 20 minutes, then remove the weights and bake again for 5-10 minutes, or until golden brown. Cool.