Ingredients
2¼ cups all-purpose flour
1 tablespoon cornstarch
1 teaspoon baking soda
1 teaspoon salt
¾ cup unsalted butter, melted and slightly cooled
1 cup packed light brown sugar
⅔ cup granulated sugar
2 large eggs, at room temperature
1 tablespoon vanilla extract
2 cups semisweet chocolate chips, divided
Instructions
Preheat and prepare the pan
Set your oven to 350°F. Line an 8×8-inch square baking pan completely with parchment paper, leaving overhang on two opposite sides to act as handles for lifting the bars out later.
Whisk dry ingredients
In a medium bowl, combine the all-purpose flour, cornstarch, baking soda, and salt. Whisk together thoroughly and set aside.
Combine melted butter and sugars
In a large bowl, add the melted butter, light brown sugar, and granulated sugar. Whisk vigorously for about 30 seconds until the mixture forms a thick, somewhat gritty slurry.
Add eggs and vanilla
Add the room-temperature eggs and the vanilla extract to the butter-sugar mixture. Whisk continuously for about 1 minute until the mixture is smooth, glossy, and well combined.
Mix wet and dry ingredients
Pour the dry ingredients into the wet mixture. Use a rubber spatula to fold and stir until the flour is almost fully incorporated. A few streaks of dry flour remaining is acceptable.
Add chocolate chips
Reserve ¼ cup of the chocolate chips for the topping. Stir the remaining 1¾ cups of chocolate chips into the dough until evenly distributed.
Transfer to the pan
Dollop the dough into the prepared baking pan. Use an offset spatula or the back of a spoon to spread the dough into an even layer, leaving a slightly textured top surface. Sprinkle the reserved ¼ cup of chocolate chips evenly over the top.
Bake
Bake for 55 minutes, or until the edges are set and golden brown and a toothpick inserted into the center comes out with a few moist crumbs (not wet batter). The center will still be slightly soft. For a gooier, fudgier texture, reduce baking time to 45 minutes.
Cool and cut
Let the bars cool in the pan for 1 hour. Using the parchment overhang, lift the entire slab out of the pan and transfer it to a cutting board. Use a large, straight-edged knife to cut into 16 bars (4 rows by 4 rows), wiping the blade clean between cuts. Serve at room temperature
