Although I already have a tofu-based recipe I use regularly to make sour cream, I decided to try the "Tofu Sour Cream" (page 574) to see which I liked better. The recipe in this book calls for oil, and surprisingly (at least to me) for a small amount of tahini. I'm guessing the tahini adds body and thickness to the sour cream, and just a little extra richness as well. I omitted the oil, but I did include the tahini. The "sour" comes from fresh squeezed lemon juice, and adds the perfect amount of tang. In my own recipes for tofu mayonnaise and sour cream, I usually add about ½ teaspoon guar gum to keep the finished product from separating as it sits. I decided to forgo the guar in this preparation, as I felt the tahini would provide the same quality.
I have to say, I really notice the flavor of the tahini in this sour cream, even with the small amount called for. I like tahini, but I'm not sure if I like the flavor of it in sour cream. I think one could leave it out altogether, and still end up with a very nice tofu sour cream. It's probably a matter of personal preference and taste. Give it a try and see what you think - I'd be very interested in your thoughts!