then separate the thick clotted cream on the top from the thin liquid (whey?) left behind.
It's buttermilk, just use it to make the scones.
Only problem is that's 3 days until you can have your scones, buying a tub of Rodda's is far easier :)
But for those of us who live in uncultured parts of the world where clotted cream isn't available in the shops, making your own is the only option. Doesn't take 3 days, though. The initial cook works very well if done in the oven overnight.