Chewy Chocolate Chip Bar Cookies

Instructions

1. 1

   Heat the oven and build a parchment sling

   Set a rack in the center of the oven and heat it to 350°F (177°C). Lightly grease a 9x13-inch metal baking pan, then lay in a sheet of parchment that runs the length of the pan and hangs over the two long sides by an inch or two. Those overhangs are your handles later — you'll lift the whole slab out in one piece and cut it on a board instead of hacking at it in the pan. Light-colored metal is the pan to reach for; dark metal and glass both run hotter and will darken the edges before the middle sets.

2. 2

   Whisk the dry ingredients

   In a medium bowl, whisk the flour, cornstarch, baking soda, and fine sea salt together for a good 15 seconds, until it looks uniform. Measure the flour by spooning it into the cup and leveling off with a knife, or weigh it — scooping straight from the bag can pack in an extra ounce or more, which is the single most common reason bar cookies come out dry and cakey. The cornstarch is a small addition that softens the crumb and keeps the bars tender for days.

3. 3

   Whisk the butter and sugars

   In a large bowl, whisk the melted butter with both sugars until the mixture is glossy and smooth with no lumps of brown sugar left, about 30 seconds of vigorous whisking. Make sure the butter has cooled for a few minutes first — if it's still hot it will start cooking the eggs. There's no creaming here and no mixer needed, which is exactly why these bars bake up dense and chewy rather than puffy and cake-like.

4. 4

   Add the eggs and vanilla

   Whisk in the whole eggs one at a time, then the extra yolk, then the vanilla. Keep whisking for another 20 seconds or so until the batter turns a shade lighter and looks silky and emulsified. That lone extra yolk is doing quiet work — the added fat and emulsifiers give the bars their soft, bendy chew.

5. 5

   Fold in the flour and the chocolate

   Switch to a flexible spatula and add the dry ingredients all at once. Fold just until a few dry streaks remain, then add 1 3/4 cups of the chocolate chips and fold until everything is barely combined. Stop there. The dough will be thick, soft, and a little slick from the melted butter — that's right. Overmixing at this stage builds gluten and firms the bars up more than you want.

6. 6

   Press into the pan

   Scrape the dough into the pan and press it into an even layer with the spatula or lightly dampened fingertips, working it all the way into the corners. An even thickness matters more than a perfectly smooth top, since thin spots will overbake. Scatter the remaining 1/4 cup of chips over the surface and press them in lightly, nudging any that have landed right at the pan edge back toward the center so your cut edges stay clean.

7. 7

   Bake until the edges set and the center is still soft

   Bake for 24 to 28 minutes. You're looking for edges that are golden and just beginning to pull from the sides, and a center that is puffed, matte, and set but still noticeably soft when you nudge the pan. A toothpick in the middle should come out with a few moist crumbs, not wet batter. Pull them while the middle looks slightly underdone — residual heat finishes the job, and these go from chewy to crumbly in about three extra minutes.

8. 8

   Cool completely, then cut

   Set the pan on a wire rack and let the bars cool all the way through, at least 2 hours. Cutting warm bars gives you ragged edges and smeared chocolate, and they'll taste underbaked because the structure hasn't finished firming. When they're cool, lift the slab out by the parchment and cut 4 across by 6 down with a long sharp knife, wiping the blade between cuts. Sprinkle with flaky salt if you like, right after cutting.

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Baker's Tips

• 1.

  Weigh your flour if you can. 360g is 360g; a 'cup' can vary by 20% depending on how you fill it, and bar cookies show that variance more than almost anything else you bake.

• 2.

  Light-colored metal is the ideal pan. Glass insulates and bakes slowly, so add 3 to 5 minutes and watch the center; dark metal browns the bottom fast, so check at 22 minutes.

• 3.

  Pull them early rather than late. Bars keep baking in a hot pan for several minutes after they leave the oven, so slightly-underdone-looking is the target.

• 4.

  For a deeper, butterscotchy flavor, brown the butter first: cook it until the milk solids turn golden and smell nutty, then cool it for 10 minutes and add a tablespoon of water back to replace what evaporated.

• 5.

  Chill the cooled slab for 20 minutes before cutting if you want bakery-sharp edges. A long knife wiped clean between cuts does the rest.

• 6.

  The chocolate is easily swapped — chopped dark chocolate, chunks, M&M's, butterscotch chips, or half chocolate and half toasted pecans all work at the same 2-cup total volume.

• 7.

  Doubling doesn't mean one bigger pan. Make two separate batches in two 9x13 pans, since a deeper layer of dough will overbake on the outside before the middle ever sets.

Equipment

• 9x13-inch light-colored metal baking pan
• Parchment paper
• Large mixing bowl
• Medium mixing bowl
• Whisk
• Flexible silicone spatula
• Kitchen scale or dry measuring cups
• Wire cooling rack
• Long sharp knife and cutting board

Storage