Place the bowl and blade of a food processor into the freezer to chill for 4 to 5 hours.
Refit the bowl and blade, turn on the food processor, and pour the cream through the feed tube. Continue to process for about 10 minutes, until the Butter has hardened around the blade, leaving the liquid that has separated from the cream in the bottom of the bowl.
Transfer the Butter to a fine sieve and shake 2 or 3 times over the sink to allow any excess liquid to drain.
Put the butter in a bowl, cover, and chill for at least 1 hour before using.
Store it in the refrigerator, where it has a shelf life of about 1 week.
While holding the ruler, grab the end of the top layer of wax paper and slowly pull it toward you; this will form the Butter into the shape of a log.