Cream the butter and sugars: In a large bowl, beat softened butter, brown sugar, and granulated sugar for 2–3 minutes until light and fluffy. This traps air for lift and chewy edges.
Add eggs and vanilla: Mix in the egg, egg yolk, and vanilla until smooth.
Scrape the bowl so everything combines evenly.
Whisk dry ingredients: In a separate bowl, whisk flour, cornstarch, baking soda, and salt.
Combine gently: Add the dry ingredients to the wet in two additions. Mix on low just until no dry streaks remain. Do not overmix.
Fold in chocolate: Stir in chips and chunks.
The combo gives you both structure and melty pools.
Chill briefly: Cover and chill the dough for 30–45 minutes. This helps prevent spread and deepens flavor.
Preheat and prep: Heat oven to 350°F (175°C). Line baking sheets with parchment.
Scoop: Use a 2-tablespoon scoop to portion dough.
Roll into balls and place 2 inches apart. Press a few extra chips on top for bakery looks.
Bake: Bake 9–11 minutes until edges are set and centers look slightly underdone. They’ll finish on the sheet.
Finish: Tap the pan once on the counter to help the cookies settle.
Sprinkle with flaky salt if using. Cool 5 minutes on the sheet, then move to a rack.