-
Whisk together flour, baking powder, and salt in a medium bowl.
-
Beat butter and sugar in a large bowl using an electric mixer on high speed until light and fluffy, about 3 minutes.
-
Add the tahini and vanilla and beat to combine.
-
Reduce speed to low and add flour. Mix until just combined (you will have a crumbly dough).
-
Press dough into a disk and wrap in plastic wrap. Chill dough until firm, about 1 hour or up to 24 hours.
-
Put oven racks in upper and lower thirds of the oven. Preheat oven to 350 degrees F. Line two baking sheets with parchment or non-stick liners.
-
Stir together sesame seeds and sugar and spread out on a small plate.
-
Roll dough into 24 balls of equal size. Roll balls one at a time in seeds to coat. Place rolled balls 2 inches apart on baking sheets.
-
Bake cookies for 12 to 15 minutes, rotating halfway through, until puffed and starting to crack.
-
Cool cookies on baking sheets for 10 minutes. (Cookies will easily break when hot). Carefully transfer cookies to a wire rack and cool completely.