Preheat your oven to 350ºF. Line a 9"x13" ¼ sheet pan with parchment paper so there is 1" of overhang on all sides.
Sift together the flour, cocoa powder, and salt to remove lumps and then set aside.
Melt your butter, oil, and chocolate together in a heatproof bowl over simmering water. Whisk occasionally until the butter is melted then remove from the heat.
In a large heatproof bowl, whisk together your white sugar, brown sugar, vanilla, and room temperature eggs in a bowl until thick and glossy or whip on your stand mixer for about 4 minutes on medium-high.
Add your hot melted chocolate mixture to the egg/sugar mixture and whisk for one minute or until the sugar is dissolved. Rub the mixture between your fingers, if you can still feel granules then keep whisking. If your mixture is no longer warm, you can return the bowl to your pot of simmering water and whisk for another minute until the granules are dissolved. This is what makes the crackly crust.
Add in the flour mixture and chocolate chips to the egg mixture and fold gently until just combined. Don't over-mix it.
Pour your batter into the parchment-lined pan. Place the pan in the center of the oven and bake for 18-20 minutes or until a toothpick comes out from the center with a few sticky moist crumbs.
Let your brownies cool until the pan is barely warm before removing the parchment paper and slicing the brownies.
I'm using a 9"x13" (¼ sheet) pan with parchment paper (not wax paper)Make sure you mix your chocolate/egg mixture until you don't feel any granules of sugar anymore or your brownies will be dull looking on top and not crackled. This recipe makes 18 brownies that are 2"x3" in sizeThe best way to cut brownies is to use a plastic or ceramic knife, no sticking! Store leftover brownies in an airtight container or ziplock bag at room temperature to keep them soft and moist.