Get your hands on the freshest, highest quality heavy whipping cream you can. We are lucky enough to get our milk delivered fresh to our home every Thursday. I also want to point out that my Cuisinart is almost old enough to be called vintage. I inherited it from a friend about fifteen years ago. All I had to do was purchase a new blade. It has two speeds: on and off. I have found that it's all I really need.
I digress. Put about two cups of the cream in the food processor. Process past the point of whipped cream and if you are watching through the feed tube, you will see it "break". This takes more than a few minutes.
A thin , cloudy liquid, actual buttermilk, will start to pool in the bottom of the food processor as your butter gets firmer and firmer. Pour this off and commence the enjoyment of drinking it.
When your butter is quite firm and sort of in a ball and there is no more liquid in the bottom to pour off, you are ready to "wash it". This part of the process is essential to clarifyin the flavor and will help your butter "keep".
You will need ice water at the ready. Add about a cup of water (no ice) to the food processor and run for several seconds, then pour it off. Repeat this process until the liquid you are pouring off is pretty clear.
At this point you are ready to add salt and any other flavors. For this batch, I moved the butter to a stainless steel mixing bowl and added sea salt and the zest of two lemons. Knead it thoroughly to distribute any additives and you are ready to roll it into a log, wrap in plastic wrap and put in the fridge or freezer.
I sliced off a few thin coins and added them to the leftover green bean/cherry tomato pasta...YUM. I think it would be great on fish or rubbed under the skin of a chicken to be roasted.