1 tablespoon Cultured buttermilk, or plain whole milk yogurt.
1/2 teaspoon Fine ground sea salt, optional
Pour heavy whipping cream into a clean quart-sized jar and add 1 tablespoon of the cultured buttermilk or yogurt. Mix well with a clean utensil, and cover jar loosely with a lid or a clean cloth.
If culturing the cream with buttermilk place the jar in a warm place in your kitchen. If you are culturing the cream with yogurt, you will need to place your jar in a warmer place. For example, you can place your jar in your oven, keep your oven turned off. Yogurt temperature should get to warm. Room temperature.
Allow the cream to culture anywhere from 8 to 48 hours. Once you achieve the desired level of taste, transfer the cultured cream to the device you will be using to whip it, such as a stand mixer. Whip the cream until butter forms and a white liquid is left in the bottom of the mixer bowl. The white liquid is pure buttermilk.
Using a mesh strainer with cheesecloth or a flour sack towel and place the lined strainer over a large bowl. Strain the butter and buttermilk through the lined strainer. Pull the cloth together and squeeze out as much buttermilk as possible from the butter.
Put the butter in a clean bowl and cover it with cold purified water. Press the butter with a spatula to release any bits of remaining buttermilk. The water will become cloudy. Pour off the water and repeat this process until the water is clear and no more buttermilk can be pressed out of the butter. Drain water. Press the butter to release any remaining water and pour it out of the bowl.
Add salt to the butter and work it into the butter.
Transfer the butter to a surface covered with parchment paper or plastic wrap. Shape butter and refrigerate. The butter should remain fresh for approximately two weeks.
