Step 1

1 In a small bowl, stir together the flour and baking soda

Step 2

2 In the bowl of a stand mixer fitted with the paddle attachment, or using a large bowl and a hand mixer, beat together the butter, brown sugar, granulated sugar and salt for a few seconds on low speed and then on medium for about 1 minute, just until thoroughly combined (the mixture should not be fluffy)

Step 3

3 Add the egg, tahini and vanilla, and beat on medium speed just until smooth, about 30 seconds

Step 4

4 Scrape down the bowl after the first 15 seconds to make sure the ingredients fully incorporate

Step 5

5 Add the flour mixture, and mix on low speed until the dough just comes together

Step 6

6 Do not overmix, and stop as soon as there are no dry patches

Step 7

7 Using a spatula, scrape down the bowl and give the dough a fold or two by hand to make sure there are no unmixed parts

Step 8

8 Cover and refrigerate for at least 1 hour, and up to 24 hours

Step 9

9 Once the cookie dough is ready, position a rack in the middle of the oven and preheat to 375 degrees

Step 10

10 Line 2 large, rimmed baking sheets with parchment paper

Step 11

11 Scoop the dough into 38 smooth balls, using a No, 50 disher or slightly heaping tablespoon (each ball should weight about 20 grams)

Step 12

12 Roll the balls generously in the sesame seeds, roll again between your hands to make sure the seeds stick, and place them a couple inches apart on the lined baking sheets (about 12 per sheet — they will spread, but not dramatically)

Step 13

13 Bake one sheet at a time for about 10 minutes, just until the cookies are puffy, light brown and a little crackly

Step 14

14 Remove from the oven, set a kiss in the center of each one (embed by slightly stamping it in) and return to the oven for 2 minutes, or until the cookies are golden brown and slightly flatter, and the chocolate has softened but still holds its shape

Step 15

15 Carefully slide the parchment off the pan and let the cookies cool on the countertop

Step 16

16 The chocolate should firm up after a couple hours, just about to the consistency of room temperature-set ganache

Step 17

17 They should not regain the snap of tempered chocolate — soft is preferable here