Add the flour, sugar, and salt to a food processor, and pulse a few times to combine. Add the butter and pulse until the mixture resembles fine breadcrumbs with pea-sized pieces.

Add the egg, and pulse until the dough starts to come together.

Do not process to the point that a large ball of dough is formed. The dough should be quite crumbly with large clumps, and should stick together when you press a piece between your fingers.

Transfer the dough to a lightly floured surface, and gather into a ball. Shape the dough into a 1-inch thick disc. Wrap tightly in clingfilm, and refrigerate for at least 1 hour before use.