Prep your pan and oven. Line two large baking sheets with parchment paper. Preheat the oven to 350°F (175°C).

Cream the butter and sugars. In a large bowl, beat the softened butter with the brown and granulated sugars for 2–3 minutes until light and fluffy. This step adds air for thickness.

Add eggs and vanilla. Mix in the eggs one at a time, then add vanilla. Beat until smooth, scraping the bowl as needed.

Whisk dry ingredients. In a separate bowl, whisk together flour, cornstarch, baking powder, baking soda, and salt.

Combine wet and dry. Add the dry ingredients to the butter mixture. Mix on low just until a thick dough forms. Do not overmix.

Fold in chocolate. Stir in the chocolate chips/chunks. Save a handful to press on top before baking for a bakery look.

Portion thick scoops. Use a large cookie scoop (about 1/4 cup per cookie) or weigh to 80–100 grams each for true bakery size. Roll into tall, slightly rough balls. Place 6 per sheet to allow space.

Chill briefly. For best thickness, chill the portioned dough balls in the fridge for 20–30 minutes. If you’re in a hurry, you can bake right away, but they’ll spread a bit more.

Bake. Bake for 11–14 minutes, until the edges are set and the centers look slightly underbaked and puffy. They’ll continue to set on the sheet.

Finish and cool. Immediately press a few extra chocolate chips on top and sprinkle with flaky sea salt if you like. Let cookies cool on the sheet for 10 minutes, then move to a rack.