Combine flour, salt and sugar. Rub in butter with your fingertips until the mixture resembles breadcrumbs. Add egg yolk and water and knead to form a ball. Wrap the in cling film and chill in the fridge for at least 1 hour.
Preheat oven to 180 C / Gas 4. Grease and flour a tart tin, up to 30cm in diameter.
Dust work surface and rolling pin with a little flour and roll out the pastry to about 5mm thick. Roll up on the rolling pin to transport to the prepared tin. Gently place the pastry into the tin, pressing down with your fingers to evenly cover the bottom and sides of the tin. Roll the pin over the edges of the tin and remove any excess pastry. Crimp the edges with your fingers.
Prick the bottom with a fork, cover with baking parchment and fill with dried beans or lentils. (This is called blind baking and is done so the pastry case does not swell or bubble up whilst baking.)
Bake in the preheated oven for 30 minutes, or till lightly browned on the edges. Remove from oven, then remove the parchment and beans (you can cool the beans and reserve them for later use). Allow the pastry case to cool completely before filling.
If you use a smaller tin, about 20cm in diameter, you will have enough pastry to make an additional six mini pastry cases. You could easily freeze the mini pastry cases after baking; be sure to cool completely before freezing and defrost at room temperature.