Fifteen Kilograms of Imperfect Lemons

You can get starter cultures from the internet or Facebook sharing groups.

For crème fraiche, you put a teaspoon of the culture in a 220ml jar of cream and leave out for 24 hours. Then refrigerate. To re-make it, you need to do this again within 3-5 days of making it, otherwise you can freeze a teaspoon of it. Best before 7 days for making it.

Buttermilk is the same except you use milk instead of cream.