In a large bowl, or bowl of a stand mixer (fitted with paddle attachment), cream the butter, tahini, and sugars. Beat on medium speed for 3-4 mins, scrape down the bowl 1-2 times during the creaming process. Add the egg, egg yolk, and vanilla and beat until combined.
In a medium bowl whisk the salt, soda, powder, and flour. Transfer to the wet ingredients and mix till combined.
Mix in the chocolate chips with a spatula. Cover the bowl and refrigerate for 12 hours (helps bind the cookies).
Remove from fridge, scoop into 2 T sized balls (will make about 14-18 balls).
Place on parchment lined baking sheet and bake at 325°F for 13-15minutes. Cookies are done when the edges are getting lightly golden brown but still pale in the middles. Remove, let rest on sheet for 5 mins then transfer to a wire rack to cool completely.
Notes
To amp up the flavors even more, brown the butter. Let it solidify before creaming it with the tahini and sugars. Mix up the tahini prior to measuring and adding it to the bowl. You want to be sure any of the juices that may have separated are well incorporated.Store cookies in an airtight container at room temperature for 3-4 days.