Pour heavy cream into a large bowl and add in the yogurt, stir to combine
Cover with a dish towel and let it sit at room temperature for about 48 hours
Pour the mixture into a stand mixer and whisk on medium until you have butter
Strain the buttermilk into a bowl
Put the butter into a bowl of ice water
Squeeze out excess buttermilk
Do another round of the ice water and squeeze again until water is clear
Add sea salt, to taste and mix well
Form into a ball, wrap in parchment paper or place in an airtight container and store in the fridge
