Combine dry ingredients. Whisk together oat flour, baking soda, baking powder and salt in a small bowl. 3 cups (280 g) oat flour 2 teaspoons cornstarch 1 teaspoon baking soda ½ teaspoon salt
Combine butter and sugars. In a large bowl Whisk butter, granulated sugar, and brown sugar until combined. ¾ cup (1 ½ stick, 170 g) unsalted butter ½ cup (100 g) granulated white sugar ¾ cup (160 g) packed light brown sugar
Add vanilla and eggs. Add egg and egg yolk, one at a time whisking to combine. Add vanilla and mix just until combined. 1 large egg 1 large egg yolk 2 teaspoons vanilla extract
Add dry ingredients. Gradually stir in flour mixture so they wouldn’t spoon or spatula. Stir in chocolate chips. Cover and chill cookie dough for at least 2 hours, ideally overnight for best texture. 1 ½ cups (255 g) semi-sweet chocolate chips
Preheat and prepare cookie sheets. When ready to bake, preheat the oven to 350°F (180°C). Line two cookie sheets with parchment paper (or a silicone baking mat). Take cookie dough out of the fridge and let soften for several minutes to allow for easier scooping.
Scoop the cookies. Using a 1-inch cookie scoop or a tablespoon, scoop the cookies into 1 ½ inch balls onto prepared cookie sheets about 2 inches apart.
Bake and cool cookies. Bake the cookie sheet on the middle rack for 9-11 minutes, until lightly browned on the sides. The centers will still look soft. Remove from the oven and let cool on a baking sheet for 5 minutes before transferring to a wire rack to cool completely.