The Recipe -
2 cups of Peanuts, salted and roasted (in other words, peanuts you buy most anywhere.)
1.5 teaspoons of some type of oil. I’ve seen vegetable, peanut and olive recommended — we used Olive Oil.

Add half of the peanuts and half the oil to a food processor. Use a metal blade, and let it run for approximately 2 minutes. Then add the remainder, and mix for another 2 minutes. If you want thinner peanut butter, let it run for longer, or you can add a little more oil. Be very careful, as a little additional oil really thins it out. It will thicken when you put it in the refrigerator.

According to what I’ve read, it will keep for approximately three weeks.