01 -
Preheat the oven to 163°C (325°F). Line an 8x8-inch light-colored metal pan with foil or parchment paper and spray with nonstick cooking spray.
02 -
In a microwave-safe bowl, add the butter and sugar. Microwave for about 1 minute, or until the butter is melted.
03 -
Whisk in the eggs, egg yolk, and vanilla. Stir in the vegetable oil and cocoa powder.
04 -
Using a rubber spatula, stir in the all-purpose flour, cornstarch, and salt until combined. Then stir in the semisweet chocolate chips.
05 -
Spread the brownie batter evenly into the prepared pan. Bake for 30 minutes or until the brownies are set and a cake tester inserted into the center has moist crumbs attached. Do not overcook.
06 -
Let the brownies cool completely to solidify before cutting and serving.
07 -
Store brownies in an airtight container at room temperature for up to 3 days. Serve warm for gooey brownies, at room temperature for chewy brownies, or chilled for a fudgy texture.