Make Ahead Tip: Prepare through Step 2; cover and refrigerate potatoes and sauce separately. Finish Step 3 and hold at room temperature for up to 2 hours or refrigerate for up to 8 hours.
Tahini is a thick paste of ground sesame seeds. Look for it in large supermarkets in the Middle Eastern section or near other nut butters. Sadaf is one of our favorite brands--it's nutty, creamy and never bitter.