We love this recipe – a true two-in-one. First, you make the butter using double cream and, second, in doing so, find yourself with the buttermilk you need to make the scones. Perfect! Make sure you have space in your freezer to chill the butter quickly – it’s not essential (you could use the fridge), but it helps speed things up.
Make the butter. Pour the cream into the bowl of a stand mixer fitted with the whisk attachment and whisk on medium speed until thick.
Continue whisking until the cream collapses and the buttermilk separates from the butter in the bowl.
Set the muslin-lined sieve set over a bowl and pass the mixture through it – the liquid is the buttermilk. Measure out 150ml of the buttermilk for the scones.
Place the butter in the sieve back into the mixer bowl and whisk for a further 1 minute to drain any excess buttermilk, then drain it once more.
Place the drained butter in a bowl and knead the salt into it. Spoon some of the butter into a ramekin and smooth the top, then place in the fridge to chill.
Spread out the remaining butter on a sheet of baking paper so that it is about 1cm thick. Cover with another sheet of baking paper, then freeze for 15 minutes until firm.
Once the butter is firm, use it to make the scones. Heat the oven to 220°C/200°C fan/425°F/Gas 7.
Sift the flour, salt, baking powder and mustard powder into a large bowl.
Rub the pieces of butter into the flour mixture using your fingertips until the mixture resembles breadcrumbs, then stir in the parmesan and chives. Make a well in the centre of the mixture and pour in the buttermilk. Using a table knife, mix to a soft dough. Tip out the dough onto a lightly floured surface and knead until smooth.
Roll out the dough until it is 2.5cm thick and cut it into 8 rounds using the 6cm round cutter, re-rolling the trimmings as necessary. Place the rounds on the floured baking sheet and brush the tops with beaten egg.
Bake the scones for 12–15 minutes, until risen and browned, then transfer them to a wire rack and leave to cool slightly. Serve the scones warm with the chilled butter for everyone to help themselves.