Preheat your oven to 375°F and position a rack in the center for even baking. Prepare a light-colored baking sheet by lining it with a silicone baking mat. This setup yields cookies that spread just enough and bake with soft centers and crisp, golden edges. Avoid dark metal pans, as they can cause overbaking and excessive spreading, especially without a silicone liner.
In a medium-sized mixing bowl, combine the softened butter and brown sugar. Use an electric hand mixer on medium speed to cream them together until the mixture is airy and pale—this step should take at least a full minute. Proper creaming is key for forming those signature cookie crackles.
Add in the egg yolk and vanilla extract, mixing until smooth and fully incorporated.
Sprinkle the flour evenly over the butter mixture, followed by the sea salt, baking soda, and baking powder. Mix on low until a cohesive dough forms and no streaks of flour remain.
Fold in the chocolate chips and chocolate chunks gently with a spatula, ensuring even distribution throughout the dough.
Portion the dough into 10 equal scoops and place them spaced apart on the prepared baking sheet. For neater, uniform cookies, roll each scoop into a smooth ball between your palms.
Bake for 9 to 10 minutes, just until the edges are turning golden. The cookies may look slightly puffed when you take them out of the oven—that’s normal. As they cool, they’ll deflate slightly, developing a crackled top and a chewy texture inside.
Let the cookies rest on the baking tray for 5 minutes to firm up, then transfer them to a wire rack to cool completely before serving.