TO DEVISE A PROPERLY CHEWY BROWNIE RECIPE, WE FIRST HAD TO DISCOVER THE PERFECT RATIO OF OIL TO BUTTER. WE THEN COMBATED GREASINESS BY REPLACING SOME OF THE OIL WITH EGG YOLKS, WHOSE EMULSIFIERS PREVENT FAT FROM SEPARATING AND LEAKING OUT DURING BAKING. WE FOUND THAT UNSWEETENED CHOCOLATE PROVIDES THE STRONGEST CHOCOLATE FLAVOR. FINALLY, FOLDING IN BITTERSWEET CHOCOLATE CHUNKS JUST BEFORE BAKING GAVE OUR CHEWY BROWNIES GOOEY POCKETS OF MELTED CHOCOLATE AND ROUNDED OUT THEIR COMPLEX FLAVOR.
MAKES TWENTY-FOUR 2-INCH BROWNIES
For the chewiest texture, it is important to let the brownies cool thoroughly before cutting. If your baking dish is glass, cool the brownies 10 minutes, then remove them promptly from the pan (otherwise, the superior heat retention of glass can lead to overbaking). While any high-quality chocolate can be used in this recipe, our preferred brands of bittersweet chocolate are Callebaut Intense Dark Chocolate L-60-40NV and Ghirardelli Bittersweet Chocolate Baking Bar. Our preferred brand of unsweetened chocolate is Scharffen Berger. Leftovers can be stored in an airtight container at room temperature for up to 4 days.
1. Adjust oven rack to lowest position and heat oven to 350 degrees. Referring to directions in Making a Foil Sling (related), make sling using the following steps: Cut 18-inch length foil and fold lengthwise to 8-inch width. Fit foil into length of 13 by 9-inch baking pan, pushing it into corners and up sides of pan; allow excess to overhang pan edges. Cut 14-inch length foil and fit into width of pan in the same manner, perpendicular to the first sheet (if using extra-wide foil, fold second sheet lengthwise to 12-inch width). Spray with nonstick cooking spray.
2. Whisk cocoa, espresso powder (if using), and boiling water together in large bowl until smooth. Add unsweetened chocolate and whisk until chocolate is melted. Whisk in melted butter and oil. (Mixture may look curdled.) Add eggs, yolks, and vanilla and continue to whisk until smooth and homogeneous. Whisk in sugar until fully incorporated. Add flour and salt and mix with rubber spatula until combined. Fold in bittersweet chocolate pieces.
3. Scrape batter into prepared pan and bake until toothpick inserted halfway between edge and center comes out with just a few moist crumbs attached, 30 to 35 minutes. Transfer pan to wire rack and cool 1½ hours.
4. Using foil overhang, lift brownies from pan. Return brownies to wire rack and let cool completely, about 1 hour. Cut into 2-inch squares and serve.