Optional: roast the peanuts on a cookie sheet for 10 minutes at 350 degrees F. Or, purchase pre-roasted peanuts that have been shelled. Toasting the peanuts helps bring out more flavor and loosens the oils in the peanuts making it easier to blend into peanut butter.
Place the peanuts in the food processor with the blade attachment. Pulse for 30 second intervals or until chopped. For chunky peanut butter, remove 1/2 C of the chopped peanuts and set aside.
Run the food processor continually for another minute. Stop, and scrape down the sides. The peanut butter will go from chopped nuts to a clumpy glob - keep going! Don't get discouraged.
Process for another minute. Scrape down the sides as needed - at this point the peanut butter will start to become glossy and soft.
Add the oil, salt, and sweetener. If using extras (cinnamon, cocoa), then use at this time.
Process for an additional 2 minutes or until the peanut butter becomes completely smooth. If you are going for chunky peanut butter, fold in the chopped peanuts you reserved previously. Add additional salt to taste, if necessary.
Transfer the peanut butter to a storage container, cover and refrigerate until ready to use.