Add cream and plain yogurt to a bowl, and mix until well combined. Cover with plastic wrap and leave at room temperature for 24 hrs. Refrigerate for approx. 2 hrs., then beat with a hand mixer until butter and buttermilk separate.
Strain buttermilk through a sieve. Add ice cubes and cold water to a large bowl to make an ice bath, and knead butter inside of it. Once the butter is compact, transfer to parchment paper and compress it into a small block or any other shape you like. Enjoy on bread or use for cooking and baking!