Cultured butter is made from cream that has been lightly fermented with live cultures.
you'll need heavy cream and fresh yogurt (unflavored, with live cultures.) If you've got no yogurt, kefir yogurt or sour cream can be used too, just ensure what you use contains live cultures
Pour cream into a bowl and add in yogurt. Stir it together, cover, and leave it at room temperature to sit and do its thing. At least 36 hours, but it can be as long as 48 hours too.
Once fermented it's time to whisk. Start on low-medium speed, whisking until the cream thickens. This part can get a bit messy, especially as the butter starts to split from the buttermilk.
Tip the mixture into a colander over a bowl to catch the butter milk. Save the buttermilk in a jar in the fridge or the freezer to use later on
Rinse the remaining butter in the colander under cold water, then pop it into a bowl of ice-cold water. Use your hands to squeeze and knead the butter to remove the remaining buttermilk.
Use cold butter paddles or wooden spoons to flatten and squash the butter, over and over again. This removes those last remaining drops of buttermilk.
Portion the butter and you're done! For long-term storage the butter can be frozen.