Why This Recipe Works
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.