In a medium bowl, pour the heavy whipping cream.
Transfer the yogurt and whisk until it mixes well. Cover the bowl, set aside for about 15-18 hours at room temperature or until it becomes firm.
Chill the mixture for about 20-30 minutes in a refrigerator.
Transfer the cream to a larger mixing bowl or to the stand mixer bowl.
Attach the whisk attachment to the stand mixer or hand mixer. You can whisk the cream by using an old fashioned churn, whisk, food processor, or a blender as well.
Start beating the cream on a low speed and then to medium speed for about 8 minutes or until it forms into soft peaks.
Increase the speed a little more and whisk further until the mixture becomes thick and the buttermilk begins separating.
Add ½ cup cold water and whisk the mixture for 1 minute.
Using your hands, separate the butter to another bowl and transfer the buttermilk to a jar.
Place the butter back to a large bowl, add ½ -¾ cup cold water, and rinse the butter. Repeat the same process 3-4 times. Place all the rinsed water (buttermilk) in the jar.
Transfer the butter to a strainer and squeeze out as much buttermilk as you can from the butter.
Keep the butter in an airtight container in a refrigerator. You can add ¼ tsp salt and mix well if you wish. Store the buttermilk in an airtight jar.