1. Determine the amount of cream you will need. I use a 14-cup Cuisinart and fill it to the liquid capacity line marked on the bowl. This is about 3 1/4 cups.
2. If you can find it, buy raw cream. In Los Angeles, Whole Foods sells it. But lightly pasteurized cream works well too. The Ultra Pasteurized (Grocery Store Variety) makes a fairly flavorless butter. So choose your cream wisely. It makes a difference.
3. I like to culture the cream before I start. I do this with a big dollop of cultured sour cream. About 1 tbsp per cup.
4. Set the cream out at room temperature in a covered bowl for about 24 hrs. It should thicken, get a bit lumpy, produce a frothy layer, and change color slightly.
5. Taste it before continuing. It should be tangy, but sweet, much like crème fraise. If it tastes bad it may have gone rancid…so check it.
6. I like to work cold. So put the cultured cream back in the fridge for a few hours or a few days.
7. I like to use the Cuisinart. But a mixer works too. I use the small plastic blade attachment, but again any blade will work. Put the cream into the Cuisinart. There is a marked liquid capacity line as a guide. Turn the machine on. The cream will go through various stages: creamy, bubbly, soft whipped cream, firm whipped cream, and coarse whipped cream. Then, suddenly, the cream will change texture in a big way. The whirring will change to a sloshing. The butter is now fine grains of butter in buttermilk, and a few seconds later; a glob of pale yellowish butter will separate from milky the buttermilk. It will be very obvious.
8. The butter is fine to eat now. But with out proper washing it will go rancid in just a few days. So I recommend that you wash and work it. Add about 1/2 cup of ice-cold water. Using a fork or a pastry tool, work the water through the butter. Dump and repeat 4 or 5 times until the water you add pours off clean. There may still be suspended water in the butter so use the same tools and continue to work the butter to remove suspended water. Work until most of the water is removed. You may need to put it back into the fridge to get cold again before you get all the water out.
9. Put butter in a crock, ramekin, or roll in waxed paper.