I made butter in my food processor last week.
quart of heavy cream
annatto (extracted with oil) if desired for very yellow color
mix in food processor with multipurpose cutting blade for about 5 minutes
drain buttermilk; save for pancakes (which I made yesterday), cole slaw, etc.
add a handful of crushed ice and continue mixing for another minute and
remove butter, form ball, and knead under cold water
replace water with clean water, knead more, replace water again, repeat until water remains clear during kneading; must remove all buttermilk or it will get rancid at room temp
add 1/2 tsp salt to ball of butter (optional), knead in the salt (not under the water, the salt will wash away!); salt will double the life of the butter
add butter to a form or just leave as a ball; freeze
I got 13 oz from one quart of cream