Transfer roasted peanuts into a food processor. Add salt (optional). Blend. Depending on the food processor it can take from 5 to 20 minutes. If you have a high-power food processor like I do, no stopping or scraping sides will be needed. But if you have a regular food processor, you might need to stop and scrape the sides as needed. Be patient and continue until your butter has a silky smooth, creamy consistency,
Transfer your butter to an airtight jar.
Chop a handful of peanuts and place on top of the butter. Enjoy!
Notes
Do not add any water during the blending process. As all nuts are mostly oil, and oil and water do not mix, it will make your butter less smooth. The heat from the blender (or food processor) will soften nuts, helping them melt.
If you are using a regular blender or food processor, I would recommend warming up your peanuts slightly right before blending. It will speed up the process.