Try to find ingredients that do not have additives or stabilizers.
Pour the cream into a jar or bowl. Add 2 tablespoons yogurt. Stir gently until well combined then cover. Set the bowl in a warm (around 70*) spot. Leave it out for at least a couple of hours. Check it often and test for flavor. You want it to have a nice sour flavor but the intensity is up to you.
Beat the cream with a stand mixer or hand held until the buttermilk separates from the fat. Alternately you can place in a jar and shake firmly. Either mixing method will take quite a bit of time. As the butter separates from the buttermilk our off the liquid (save it for tomorrow’s pancakes) and continue to beat getting out as much of the buttermilk as you can.
When most of the buttermilk has been released add ½ cup very cold water and continue to mix on low. Pour off the liquid and repeat until it’s nearly clear.
While still in the bowl knead the butter by hand as you would bread dough. Pour off any remaining liquid as it accumulates. Knead in the salt. Taste and add more if desired.
At this point your butter is ready to use. I recommend reserving this special butter to be used to slather on toast and as a finishing ingredient where you’ll really be able to enjoy the flavor. It can be used in baking although the liquid content is different than conventional butter.