Tahini is a butter made out of sesame seeds. The recipe below substitutes peanut butter but any nut butter would probably work fine, but I haven't tried them so I can't say for sure. Some people just replace it with ground cumin and olive oil. I made this recipe and just left out the tahini, I didn't replace it with the peanut butter but I did put extra cumin and olive oil in it and it tasted fine. It won't taste the same for sure, it had a very mild plain flavor.