Rolling the dough in sesame seeds enhances the flavor of the tahini and gives the cookies a satisfying crunch.
Preheat the oven to 350 degrees. Line four baking sheets with parchment.
In a medium bowl, whisk together flour, baking soda, and salt; set aside. In the bowl of an electric mixer fitted with the paddle attachment, beat together butter, sugar, egg, and vanilla on medium-high speed until light and fluffy, about 2 minutes. Beat in tahini. Reduce speed to low; beat in flour mixture until just combined. Cover and refrigerate until firm, about 30 minutes.
Spread sesame seeds on a shallow dish. Scoop 2 tablespoons of dough; roll into a ball. Roll in sesame seeds until thoroughly coated, then transfer to prepared baking sheet. Repeat with remaining dough, spacing 3 inches apart. Bake, rotating halfway through, until golden brown, about 18 to 20 minutes. Transfer sheets to wire racks; let cool completely.