To make the raspberry butter, purée the raspberries in a food processor, then pass them through a fine nylon sieve, pressing with a wooden spoon so that as much juice as possible gets through – you should get about 15fl oz (425 ml).Now place the purée in a medium saucepan with the sugar and heat very gently until the sugar has dissolved.Then turn up the heat so the mixture boils rapidly for 8-10 minutes, but keep stirring from time to time so it doesn't catch on the base. When it's ready, the mixture should have reduced by one third and a wooden spoon drawn across the base of the pan should leave a trail for 1-2 seconds only, but be careful not to overcook it, or you will get glue.Then pour it into a serving dish and leave to one side to cool and set for at least an hour. For the scones, begin by sifting the flour and salt into a bowl, rub the butter lightly into the mixture until it looks like breadcrumbs, then add the sugar. Now, in a jug, beat the egg and 2 tablespoons of the buttermilk together and start to add this to the rest, mixing the dough with a palette knife. When it begins to come together, finish off with your hands – it should be soft but not sticky (if the dough seems too dry, add a little more buttermilk, a teaspoon at a time).When you have formed the dough into a ball, tip it on to a lightly floured surface and roll it into a circle at least 1 inch (2.5 cm) thick – be very careful not to roll it any thinner; the secret of well-risen scones is to start off with a thickness of no less than an inch.Cut out the scones by placing the cutter on the dough and giving it a sharp tap – don't twist it, just lift it up and push the dough out. Carry on until you are left with the trimmings, then bring these back together to roll out again until you can cut out the last scone. Place the scones on the baking tray, brush them lightly with the buttermilk and dust with a little flour.Now bake on the top shelf of the oven for 10-12 minutes, or until they are well risen and golden brown, then remove them to a wire rack to cool. Serve the scones thickly spread with raspberry butter and lots of clotted cream.