i've done it for some of my thai dishes
you need fresh roasted peanuts
and a blender works but be patient
you do not need to add any further oil
it will become a thick paste first then more liquid
well as liquid as peanut butter lol
salt is up to you
i prefer not to
i wold keep it refrigerated or in a cool dark place as it will go rancid
be warned you will go through quite a few blenders or food processors if you choose to do this frequently