Fill your jar half way with heavy cream and seal it with the lid and screw-ring. Begin shaking the jar from top to bottom for about 6-8 minutes. First it will get quiet, then it will begin to thump and slosh. Shake for :30-1 minute more. Now you have BUTTER and some buttermilk too. Open jar and sprinkle in salt to taste. Seal the jar again and shake a little bit to mix in the salt. Scoop butter out onto a plate and you’re ready to enjoy! I like the little amount of watery buttermilk that’s on the plate with your butter, but if you’d rather not have it, simply form the butter into a ball and massage and compress it with your hands under cold running water.