Sift flour, baking powder and baking soda into a medium-size bowl. Combine with kosher salt and set aside.
In a stand mixer, blend the butter, tahini and all but 1 tablespoon of the date syrup on medium speed until light, fluffy and creamy, about 5 minutes. Add the egg and vanilla, and continue to blend for another 3 minutes.
Gradually add the flour mixture and blend on the lowest speed, until just combined, occasionally scraping down the sides of the bowl with a spatula. Fold in the dates and chocolate.
Cover mixture and chill for at least 6 hours or overnight.
Preheat the oven to 325 degrees. Line a baking sheet with a silicone mat or parchment paper.
To portion out each cookie, scoop a heaping tablespoon of cookie dough into your hands. Roll into a ball and then flatten between your palms. (This is an important step — you want the cookie to be thin.)
Place onto the baking sheet and continue, leaving at least 1 inch between cookies.
Bake the cookies until the edges are golden brown, for 13 to 15 minutes. Let cool in the pan for 10 to 15 minutes.
Drizzle the cookies with the remaining syrup and a light sprinkle of Maldon salt.