I'll be honest, when it comes to brownies, I tend to favour the box mixes, mainly because I haven't found a homemade recipe that gives you that gorgeous, crackly, shiny crust. King Arthur Flour has cracked the shiny code however, and the secret is chocolate chips.
Photo by Jeffrey W.
In a series of delicious, chocolaty tests (which you can read all about by clicking the link below), PJ Hamel of King Arthur Flour found that brownie recipes with chocolate chips routinely produce shiny, delicately crispy top crusts, while those without tend to be dull and matte. The key seems to lie in the extra fat and sugar contributed by the chips, which migrates to the top and then melts to form the crust.
While a recipe specifically designed to be made with chocolate chips (such as King Arthur's Fudge Brownies) will give you the best results, chucking a couple of cups of chips into any brownie recipe (as was done with the previously chip-less Quick and Easy Fudge Brownies) will add a sheen to the top of your chocolaty treat.
How to Make Brownies With Shiny Crust: The Surprising Secret Ingredient [King Arthur Flour]