It is the fat content that determines cream's butter-making capacity - not whether or not it has been pasteurized. Commercial buttermakers concentrate cream to between 36% and 44% butterfat before they start churning. The highest concentration you can find in supermarkets in this country is heavy cream or heavy whipping cream, which can be as high as 42% butterfat, but generally is around 36%.

Once you have the cream, just shake-shake-shake it in a jar with a tight lid or overbeat it in a mixer, and you'll have butter in no time.