Preheat the oven to 350°F (180°C). Line two large cookie sheets with parchment paper. Lightly oil paper with oil spray. Set aside.
In a large bowl or the bowl of your stand mixer, add sugar, brown sugar, and margarine. Use the whisk attachment or an electric beater to beat the ingredients into a creamy mixture - it takes about 1 minute on medium speed.
Beat in plant-based milk and vanilla extract. Stop the beater.
In another bowl, whisk the dry ingredients together: flour, cornstarch, salt, and baking soda.
Sift the dry ingredients into the wet. Now swap to the paddle attachment if you are using a stand mixer, mix to incorporate and form a buttery cookie dough.
Fold in chocolate chips and beat few time to just incorporate.
Film the dough into plastic wrap and chill the dough in the fridge for at least 30 minutes to 1 hour before baking.
Scoop out cookie dough balls the size of a golf ball (about 1 1/2 tablespoons) per cookie. Roll between your hands and place on the baking sheet, leaving 3 inches as the spread while baking.
Bake for 12-14 minutes or until golden brown then cool 5 minutes on the cookie sheet before transferring to a cooling rack.
Cool at room temperature completely for 1 hour.
Store the cookies in a cookie jar for up to 1 week or freeze them in zip-lock bags for up to 1 month.