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.