1) Preheat your oven to 425°F.
2) In a large mixing bowl, combine the flour, salt, and baking powder. Add the butter and rub into the flour using your fingertips until the mixture resembles fine breadcrumbs. Stir in the sugar.
3) In a small saucepan, gently heat the milk to lukewarm, and add the optional vanilla extract and lemon juice.
4) Make a well in the dry ingredients and pour in the liquid, mixing quickly with a knife to form a soft, wet dough.
5) Turn onto a floured work surface and gently bring together to a dough, but avoid over-kneading.
6) Roll out to a thickness of about 1 inch and cut into rounds using a biscuit cutter. Place on a baking tray.
7) Brush the tops with a beaten egg to glaze and bake in the preheated oven for about 10 minutes until risen and golden.
8) Serve at room temperature with jam and high-quality butter.