Heat oven to 220C/200C fan/gas 7. Tip the flour into a large bowl with the salt and baking powder, then mix. Add the butter, then rub in with your fingers until the mix looks like fine crumbs. Stir in the sugar.
Put the milk into a jug and heat in the microwave for about 30 secs until warm, but not hot. Add the vanilla and lemon juice, then set aside for a moment. Put a baking sheet in the oven.
Make a well in the dry mix, then add the liquid and sultanas and combine it quickly with a cutlery knife – it will seem pretty wet at first. Scatter some flour onto the work surface and tip the dough out. Dredge the dough and your hands with a little more flour, then fold the dough over 2-3 times until it’s a little smoother. Pat into a round tin about 4cm deep.
Take a 5cm cutter (smooth-edged cutters tend to cut more cleanly, giving a better rise) and dip it into some flour. Plunge into the dough, then repeat until you have four scones. You may need to press what’s left of the dough back into a round to cut out another four.
Brush the tops with beaten egg, then carefully place onto the hot baking tray.
Bake for 10 mins until risen and golden on the top. Eat just warm or cold on the day of baking, generously topped with jam and clotted cream. If freezing, freeze once cool. Defrost, then put in a low oven (about 160C/140C fan/gas 3) for a few mins to refresh.