1-First Step: Prep and mise en place Preheat your oven to 350°F and line an 8×8-inch baking pan completely with parchment paper, leaving an overhang for easy removal. Measure all dry and wet ingredients. Room temperature eggs combine more evenly; take them out of the fridge ahead of time. Reserve about 1/4 cup of the chocolate chips to sprinkle on top before baking.

2-Second Step: Mix dry ingredients In a medium bowl, whisk together the all-purpose flour, cornstarch, baking soda, and salt until evenly combined. Cornstarch helps keep the bars tender by limiting gluten formation, which gives you that soft, chewy crumb.

3-Third Step: Combine butter and sugars In a large bowl, pour in the melted butter and add both the light brown sugar and the granulated sugar. Whisk vigorously for about 30 seconds until the mixture forms a thick slurry. This step dissolves the sugars into the butter for even texture and a glossy dough.

4-Fourth Step: Add eggs and vanilla Add the room-temperature eggs and vanilla extract to the butter-sugar slurry. Whisk for about 1 minute until everything is well combined and slightly aerated. This helps the dough bind together without creating a cake-like rise.

5-Fifth Step: Combine wet and dry Pour the flour mixture into the wet ingredients and fold with a spatula until the dough is almost fully combined. Avoid overmixing to keep the bars tender. Fold in the remaining chocolate chips, leaving the reserved chips for the top.

6-Sixth Step: Spread into pan Dollop the dough into the prepared pan and spread it evenly with an offset spatula. Leave a little texture on top rather than smoothing it perfectly; this helps create a pleasing crust. Sprinkle the reserved chocolate chips over the surface for a polished look.

7-Seventh Step: Bake and test Bake for about 55 minutes or until the edges are golden brown and a toothpick inserted in the center comes out with a few moist crumbs. Baking time will vary with ovens and pan type; start checking at 30 minutes if you prefer gooier bars. For a gooier center, reduce the baking time to 35-45 minutes or use a 9×13-inch pan with a doubled recipe.

8-Final Step: Cool and cut Let the cookie bars cool in the pan for about an hour to firm up sufficiently. Use the parchment overhang to lift the whole slab from the pan and place it on a cutting board. Use a clean, straight-edged knife for neat squares. Store in an airtight container to keep them soft.