• 500 ml (17 fl oz) cream
• 125 ml (4 fl oz) natural yoghurt or buttermilk

Put the cream in a pan and heat gently to blood temperature. Add the yoghurt, remove from the heat and cover tightly with plastic wrap. Leave to steep until the cream curdles and a thick layer of curd forms on top, with residual whey underneath - it will take around 24 hours will produce a thick cream. Gently remove the cream from the top with a spoon and discard the whey.