Crème Fraîche

Stir 1 tablespoon buttermilk into 50 cl (scant pint) of whipping cream in a saucepan over a gentle heat. Bring the temperature gradually up to 24°C-29°C (75°F-85°F), no hotter or it will not work; at this point the cream will still feel very slightly cool to the back of your finger.

Remove from the direct heat, pour into a bowl, cover and keep warm (at about 24°C (75°F)) either in a bath of water over the pilot light of a gas stove or in a warm airing-cupboard, etc. It will take from eight to twenty-four hours according to the temperature it is held at.