In a separate bowl, whisk together the flour, cornstarch, and baking powder. Add 1/3 of this mixture to the mixing bowl, mixing until it disappears. Add half the liquid and beat in. Scrape the bowl, then add another third of the dry ingredients and mix in. Add the remaining liquid, mix, scrape the bowl. Add the remaining dry ingredients mix until combined, scrape the bowl, and mix for one minute more.