Preheat the oven to 220C/425F/Gas 7. Line a baking tray with parchment paper or a silicone mat, and set aside.
In a large bowl, whisk together the flour, sugar, baking powder, and salt. Add the butter and, using a pastry cutter, fork, your fingertips, or a food processor, work it into the mixture until it resembles fine breadcrumbs. Stir in the buttermilk and vanilla until a soft dough is formed.
Turn the dough out onto a lightly floured surface, and roll out to a thickness of 2.5cm/1-inch.
Dust a round or fluted 5cm/2-inch cookie cutter with flour, and cut out circles from the dough. Re-roll any scraps, and cut out more circles. Transfer them to the prepared baking tray, and brush the tops with extra buttermilk.
Bake for 12 - 15 minutes until risen and golden brown. Serve warm, or cold with clotted cream, jam, or butter.