Prep the Oven & Pan: Preheat your oven to 350°F (175°C). Lightly grease an 8×12-inch baking pan with non-stick cooking spray, then line it with parchment paper leaving a slight overhang on the sides for easy removal later.
Whisk Wet Ingredients: In a medium-sized mixing bowl, vigorously whisk together the melted butter, vegetable oil, granulated white sugar, and packed light brown sugar. Add the room-temperature eggs and pure vanilla extract, then beat aggressively for a full 60 seconds until the mixture becomes pale and slightly thickened. (Note: This step is crucial for achieving that shiny, crackly brownie top!)
Fold Sifted Dry Ingredients: Sift the all-purpose flour, unsweetened cocoa powder, and salt directly into the wet mixture. Using a rubber spatula or wooden spoon, gently fold the dry ingredients into the wet mixture until JUST combined. Do not overmix, as overbeating will introduce too much air and create a cake-like texture. Gently fold in 3/4 of your chocolate chips or chunks.
Pour and Decorate: Spread the thick brownie batter evenly into your prepared baking pan, smoothing the surface with your spatula. Scatter the remaining 1/4 of chocolate chips evenly across the top.
Bake to Perfection: Bake on the center rack for 25 to 30 minutes for a perfectly moist, fudgy center. The edges should look set, but the center will still have a very slight jiggle. If testing with a toothpick, it should come out with a few wet, fudgy crumbs—not completely clean. For firmly set brownies, increase the time to 35-40 minutes.
Cool and Serve: Allow the brownies to cool completely in the pan for 15 to 20 minutes. Use the parchment paper handles to lift them out carefully, slice into 16 uniform squares, and enjoy!
