Preheat oven to 375℉. Line an aluminum baking sheet with parchment paper and set aside. In a bowl, whisk together all the dry ingredients. Set aside.
1¾ cups all purpose flour (210g), 1 teaspoon cornstarch, ½ teaspoon baking soda, ¼ teaspoon baking powder
In a separate bowl, use an electric mixer with a beater attachment to cream together softened butter (room temperature), light brown sugar, and sugar for 2-3 minutes until fluffy and lighter in color. ½ cup light brown sugar, ½ cup unsalted butter, ½ cup sugar (100g)
Mix in egg and vanilla extract until combined.
1 large egg, 2 teaspoons vanilla extract
Mix in the dry ingredient flour mixture until a cookie dough forms.
When there are still a few streaks left of flour in the cookie dough, mix in the three different chocolate chips.
⅓ cup semi-sweet chocolate chips, ⅓ cup dark chocolate chips or chunks, ⅓ cup white chocolate chips
Using a cookie scoop or large spoon, scoop evenly sized dough balls (roughly 2.3oz) and roll them into balls. Set on the prepared parchment lined baking sheet at least 2 inches apart. Add a few additional chocolate chips to the tops of the cookie dough balls.
Bake cookies for 9 minutes. Cookies should be just slightly browned on the outside and the tops should no longer look shiny, but do not overbake! Cookies will continue to bake on the hot pan when removed from the oven. Sprinkle flaky sea salt over top of the warm cookies.
Let cookies cool for 2-3 minutes before transferring to a wire rack to cool the rest of the way. Enjoy!