Add peanuts and salt to a high speed blender (or powerful food processor). Pulse a few times to get started, then put on high speed for 20 seconds. Stop, stir all the way to the bottom, and return to high speed for 30 seconds.
At this point the peanuts will be breaking down, crumbly, and churning. Continue stopping and breaking down, letting blend for 30 seconds after each stop, until extra smooth and creamy. (Vent the top of the jar you using in case it's getting too warm.)
Pour into a glass jar and store in your pantry if you plan to use within the month, or in the refrigerator if not.
Notes
*If you want to add a little sweetness, you can stir in by hand 2 teaspoons of maple syrup after you have fully processed your peanut butter. If you add it while the peanut butter is blending, it will turn grainy.