Pour the cream into the food processor bowl or a mixing bowl. Begin the mixing process.
The cream will begin to bubble and froth and eventually it will turn into whipped cream. Stop the food processor or mixer, scrape down the sides of the bowl then continue mixing.
Once the whipped cream texture begins to break, you'll notice it getting lower in the bowl. Continued mixing will cause the solid butter and the buttermilk to separate.
The cream will get thicker and then grainer. When you notice liquid in the bowl separated from the fat, it's time to take the butter out of the bowl. It takes about 10 minutes to get to this step.
Remove the butter from the from the bowl and place it in a fine mesh strainer.
Fold, press, and squeeze the butter to remove the liquid, or buttermilk. (You can save the buttermilk to use later with a buttermilk culture.)
After the buttermilk is drained and squeezed out pour ice cold water over the butter and mix/process it for a bit longer.
Pour that water out and put the butter in a flour sack cloth to absorb and drain the rest of the water/buttermilk. (I give it several squeezes, as buttermilk remaining in the butter will cause the butter to sour more quickly. Now, there is nothing wrong with eating the fermented raw butter, but I prefer my butter to taste sweet.)
Add salt to taste. This is optional. I usually don't add salt. However, adding salt helps the butter to last a little longer without fermenting.