On Cookidoo I found two recipes for butter made from fresh cream. You get buttermilk as a by-product and that's what you need as an ingredient for all kinds of goodies in the home bakery.
The butter stays in the fridge for at least three weeks to a month. The resulting buttermilk is created by separating (churning) the butter from the (acidified) cream. You can freeze it if you are not going to use it within a week.
600g pure cream
500g chilled water