Pre-heat oven to 350°F. Prepare a baking sheet with parchment paper (or silicone baking mat).
Make cornstarch “egg” by stirring together the cornstarch and water. Set aside. 2 Tablespoons cornstarch 2 Tablespoons water
Whisk together flours, baking soda, and salt into a bowl. Set aside. 1 ¼ cups (150 g) all-purpose flour ½ teaspoon baking soda ½ teaspoon salt
Using a mixer fitted with paddle attachment, cream butter and sugar together until very light, about 2-3 minutes. ½ cup (1 stick, 113 g) unsalted butter ½ cup (107 g) packed light brown sugar ¼ cup (50 g) granulated sugar
Add cornstarch mixture, and vanilla. Beat to combine. 1 teaspoon vanilla extract
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. 1 cup (170 g) semi-sweet chocolate chips
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.