Preheat your oven to 350°F (175°C). This step is crucial to ensure your cookies bake evenly.
In a large mixing bowl, whisk together the all-purpose flour, cornstarch, baking soda, salt, and baking powder.
In another bowl, use an electric mixer to cream together the unsalted butter and granulated sugar until light and fluffy, about 2-3 minutes.
Add in the large egg, large egg yolk, and pure vanilla extract to the butter-sugar mixture. Mix until well combined and smooth.
Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined.
Gently fold in the mini chocolate chips using a spatula, making sure they are evenly distributed throughout the dough.
For best results, chill the cookie dough in the refrigerator for at least 30 minutes.
Line your baking sheets with parchment paper. Scoop out balls of cookie dough and roll each ball in the granulated sugar.
Place the cookie dough balls on the prepared baking sheets, leaving enough space between each one to allow for spreading. Bake for about 10-12 minutes.
As soon as the cookies come out of the oven, sprinkle a pinch of flaky sea salt on top of each cookie. Let them cool before transferring to a wire rack.
