Pre-heat oven to 375°F. Prepare a baking sheet with parchment paper (or silicone baking mat).
Make cornstarch “egg” by stirring together the cornstarch and water. Set aside.
Whisk together flours, baking soda, and salt into a bowl. Set aside.
Using a mixer fitted with paddle attachment, cream butter and sugar together until very light, about 2-3 minutes.
Add cornstarch mixture, and vanilla. Beat to combine.
Reduce speed to low, add dry ingredients and mix until just combined, 5 to 10 seconds. Add chocolate chips and stir in, on low speed, just until combined.
Scoop cookie dough, using a 1-inch cookie scoop, and place on the prepared cookie sheet. Bake until golden brown but still soft, 10-12 minutes. Transfer sheet to a wire rack for 10 minutes, then slip cookies onto another rack to cool a bit more.