Preheat the oven to 220°C, fan 200°C, gas 7.
Mix together the flour, salt and baking powder in a large bowl. Using your fingertips, rub in the butter until the mixture resembles fine breadcrumbs, then stir in the sugar.
Mix together the milk, vanilla extract and lemon juice. Using your hands, make a well in the dry mixture, then pour in the milk mixture and bring together with a knife. Turn out the dough onto a lightly floured surface and gently knead until slightly smoother. Gently roll out to a thickness of 3cm.
Using a 6-7cm cutter, cut out 4 rounds. Bring the remaining dough together and repeat until you have 6 scones. Lift the scones onto a lightly floured non-stick baking sheet. Brush the tops with the egg. Bake for 12-15 minutes, until golden. Cool slightly, then cut in half and fill with clotted cream and jam, if you like.