Buy 1.5 to 2 Cups of roasted peanuts (no shell), unsalted.
Put in the food processor, press Start. Add salt to taste only, as it turns from coarsely ground up nuts to finely ground up nuts. It should eventually turn into a "paste" or "butter" though you might want to be prepared to add a "tich" of peanut oil toward the end to encourage smoothness. Keep refrigerated.

PS: the little handbook for my food processor has 'recipes' for nut butters and sausage and all kinds of stuff; you might want to check yours?