Sift the flour into a bowl. Add the cold butter and lightly rub into the flour using your fingertips until there are no more lumps of butter. Add the sugar, vanilla seeds and zest of 1/2 lemon. Add the egg yolk, an egg and a pinch of salt and stir to combine, then use your hands and knead until the dough starts to come just together ( it must remain crumbly, do not overwork.) Wrap the dough in a plastic wrap and place in a fridge for about 1 hour.
divide and roll out the dough
Preheat your oven to 175 °C / 350 °F. Using a sharp knife, divide dough in half and flatten into disks. Wrap half in plastic wrap and place in a fridge for up to 3 months for later use. If you are making two tarts, use both. Lightly dust a clean work surface with flour, flatten the dough into a disk and roll out the tart dough to 0.5 cm / 0.2 inch thickness.
roll out the dough
Wrap the dough around rolling pin and carefully unroll over a 24cm / 9 -inch tart plate. Prick the dough all over with the tines of a fork, and press the tines up against the edges of the tart plate. Line the dough with a large piece of parchment paper. Press the paper into the edges of the dough. Fill the parchment paper lined tart dough with pie weights or dried beans. Make sure they cover the entire space. Place in the fridge for 15 minutes.
Bake partially. First bake for 15 - 20 minutes, then check if the parchment paper sticks. If not, then remove the paper with the beans or pie weight and bake for another 10 minutes. Let the tart crust cool on a wire rack.