Preheat your oven to 350 °F (176 °C)
Spread 2 cups of peanuts (shelled) evenly on a baking sheet.
Roast for 10-15 minutes or until golden brown.
Stir the peanuts once or twice to ensure even roasting.
In the meantime, get your food processor ready; you can also use a small chopping attachment that often comes with a blender, but be careful not to overheat it.
Add 2 cups of roasted peanuts to the food processor along with the salt and, if you want to, a sweetener.
Occasionally, check if you need to scrape down the sides of the food processor with a silicone or rubber spatula.
Let the peanut butter cool a bit before adding any mix-ins (like chocolate, chili, or whatever you like).