Preheat the oven to 200ºC / 180ºC Fan / 350ºC F / Gas 6 and line a baking tray with baking paper or a silicone baking mat.
Sift the flour, bicarbonate of soda and salt into a bowl.
Rub in the cold cubed butter using your fingertips until the butter has disappeared. The mixture will still feel like fine flour since we are not using that much butter.
Stir through the caster sugar and sultanas then make a well in the centre.
Pour the buttermilk into the well and use a metal spoon to bring the mixture together.
Lightly dust your worktop or a board with flour and tip the dough out.
Bring the dough together with your fingertips, remember a light touch is essential.
If after a minute or so the mixture feels very sticky, you can add a little more flour. If it's very crumbly or dry you can add a few more drops of buttermilk or water.
It should only take a couple of minutes of kneading time until the dough comes together, it should feel soft and dry.
Put the baking tray in the oven so it's nice and hot before you put the scones on it.
Very gently roll the dough out to a thickness of 2-3cm.
Cut the scones using a 6cm round cutter. Press down but don't twist the cutter. Congratulations if you hear a little sigh as the air escapes when the dough is cut. This is when you'll know you're going to bake the tallest lightest scones you've ever seen!
Carefully tear the uncut dough away from the cut scones and place the scone rounds on to a baking tray.
Roll out the dough scraps and cut it again until you've used all the dough. You will end up with 7 or 8 large scones.
Transfer all the fruit scones on to the hot baking tray and brush the tops and sides with beaten egg.
Put the oven tray at the top of the oven if you're using a conventional oven. If it's a fan oven, the sweet spot is right in the middle.
Bake for 15 minutes until the fruit scones are risen and golden. Keep an eye on them during baking to ensure they don't over-brown.
Once baked, transfer to a wire rack and leave the fruit scones to cool off a little before smothering them with clotted cream and strawberry jam.
Best eaten fresh on the day they're baked.