In a small bowl, whisk together the flour, cornstarch, baking soda, baking powder, and salt. Set aside.
67.8 grams (1/2 cup + 1 tablespoon) All-purpose flour, 8 grams (1 tablespoon) Cornstarch, 1/4 teaspoon Baking Powder, 1/4 teaspoon Baking Soda, Pinch of Salt
In a large mixing bowl, use an electric mixer to cream together the butter, brown sugar, and granulated sugar for 3 to 4 minutes, or until the mixture lightens in color and becomes fluffy.
56 grams (4 tablespoons) Unsalted butter,, 50 grams (1/4 cup) Brown sugar, 25 grams (2 tablespoons) Granulated sugar
Add the egg yolk and vanilla extract to the creamed butter and sugar. Mix until everything is fully combined.
1 Large yolk,, 1 teaspoon Vanilla extract
Add the dry ingredients to the wet mixture along with the chocolate chunks. Mix on low speed until no streaks of flour remain. Be careful not to overmix.
50 grams (1/3 cup) Chocolate chunks + extra for topping
Line a plate with parchment paper. Scoop out 6 equal portions of dough, about 1.5 tablespoons each. Place the cookie dough balls on the plate and refrigerate for 30 minutes to help the cookies hold their shape while baking.
Preheat your oven to 350°F. Line a baking sheet with parchment paper and place the chilled dough balls onto the sheet. Bake for 10 to 12 minutes, or until the edges are lightly golden. Once out of the oven, use the rim of a bowl or a cup to gently shape the cookies into perfect circles. Sprinkle with flaky sea salt and let them cool completely on a wire rack before serving.