1) Adjust an oven rack to the middle of the oven. Preheat the oven to 350°F [180°C]. Line three sheet pans with aluminum foil, dull-side up.

2) In a small bowl, whisk together the flour, salt, and baking soda.

3) In the bowl of a stand mixer fitted with a paddle, beat the butter on medium speed until creamy, about 1 minute. Add the granulated and brown sugars and beat on medium speed until light and fluffy, 2 to 3 minutes. Add the egg, toasted sesame oil, water, and vanilla, and mix on low speed to combine. Add the flour mixture and mix on low speed until combined. Add the chocolate, if using, and mix until combined.

4) Form the dough into 3 oz [85 g] balls (¼ cup). Roll in the sesame seeds, and place 4 cookies an equal distance apart on each sheet pan. Bake the cookies one pan at a time. Bake until the dough balls have spread flat but are puffed slightly in the center, 9 minutes. Lift one side of the sheet pan up about 4 in [10 cm] and gently let it drop down against the oven rack, so the edges of the cookies set and the center falls back down. After the cookies puff up again in 2 minutes, repeat lifting and dropping the pan. Repeat a few more times to create ridges around the edge of the cookie. Bake for 15 to 16 minutes total, until the cookies have spread out and the edges are golden brown but the centers are much lighter and not fully cooked.

5) Transfer the pan to a wire rack. Let the cookies cool for 10 minutes, then move them to a wire rack to finish cooling. Store cookies in an airtight container at room temperature for 2 days (or refrigerate for up to 3 days).