Preheat the oven to 220°C, fan 200°C, gas 7. Place a baking tray in the oven to heat.
Mix the flour, salt and baking powder together in a large bowl. Using your fingertips, rub in the butter until the mixture resembles fine breadcrumbs, then stir in the sugar.
Heat the milk gently in a pan until warm, then stir in the vanilla extract and lemon juice. Using your hands, make a well in the dry mixture, then pour in the warm milk and mix together with a knife. Turn out the dough onto a lightly floured surface and gently fold over 2–3 times until slightly smoother. Gently roll out to a thickness of 4cm.
Using a 5cm cutter, cut out 4 rounds. Bring the remaining dough together and repeat until you have 8 scones. Brush the tops with the egg, then transfer to the hot baking tray. Bake for 10 minutes, until golden. Cool slightly, then cut in half and fill with clotted cream and jam.