Place softened coconut oil and sugar in a stand mixer. Beat on medium speed about 2 minutes or until evenly creamed. Mix in egg, milk, and vanilla until creamy.
In a large bowl, combine flour, baking soda, cornstarch, and salt. Add flour mixture to liquid, and beat on medium speed until a dough forms (dough will be very thick) Mix in chocolate chips.
Using your hands, smush dough into a ball and wrap in plastic wrap.* Chill 45 minutes to 1 hour or until firm. (dough may be refrigerated up to 2 days)*Alternatively, if you are baking the cookies the same day, you can shape the dough into balls right after mixing and place on cookie sheets. Chill dough balls in fridge 45 minutes or in the freezer 20 minutes prior to baking.
Shape chilled dough into 1-in balls and place 3 in apart on two parchment paper-lined baking sheets. Bake cookies at 350F 9-11 minutes or until edges just start to turn golden. (middles will still seem soft) Cool cookies on baking pan 10 minutes, then transfer to a wire cooling rack to cool completely.