Wash down all your surfaces well and wash your hands. Sterlize the equipment you will be using (I use the fluid that you get for sterlizing babies bottles) including what you will be fermenting the cream in
Take a clean saucepan and add the double cream
Over a low heat and stirring all the time, bring the cream to almost boiling point. If you have a thermometer that is around 70 degree C I have found
Once it reaches this temperature remove from the heat, place a cover on the saucepan and place into a bowl of cold water.
Leave for about 10-15 minutes or until the thermometer reads 30 - 40 degrees C.
Remove 4 desert spoonfuls of your active yoghurt and place it in whatever you wish to make your yoghurt in (a jar, the bowl from a yoghurt maker, a wide-neck flask...)
Pour a little of the warm cream into the yoghurt and stir well, removing any lumps.
Pour a little more cream in and repeat to ensure you have a smooth consistency
Add the remaining cream into the mixture and mix well
Place the cream mixture in your chosen warm place and leave for 24 hours
Once the time is up remove from the heat and place in the fridge until fully chilled