Preheat oven to 350 degrees. Using an electric mixer, beat the coconut oil, tahini, granulated sugar, and brown sugar on medium for about 3 minutes until a smooth and creamy mixture is formed. Add the plant milk and the vanilla extract and mix another minute to combine.
In a separate mixing bowl whisk together the flour, cornstarch, salt, baking powder, and baking soda to combine. Add the dry ingredients to the creamed oil and sugar mixture and mix on low speed until incorporated. Fold in the chopped chocolate.
Roll out the cookie dough onto a pan before chilling and chill in the fridge at least 30 mins or the freezer to speed it up.
Line two baking trays with parchment paper and form the dough into balls that are approximately 2 tbsp each. Place the dough balls on a tray approx 3” apart. You can bake right from fridge to oven.
Bake the cookies, one baking tray at a time, for 12-13 minutes, or until the edges are just barely golden and the entire center is just a shade lighter.
Remove from the oven and immediately sprinkle some flaked salt on top of the cookies (optional). Let cool on the baking tray. Bake the remaining cookies the same way.
Let cool and serve!