Instructions

• 1 Preheat oven to 350°F. Line an 8x8 (preferred) or 9x9 square pan with parchment paper and lightly grease it.
• 2 Place butter and brown sugar in a large microwave safe bowl. Microwave in 20 second increments, stirring between each, until the butter is completely melted. This took about 1 minute. Stir the mixture well, some of the brown sugar will begin to dissolve but not all of it. Set aside to cool for 5 minutes. Meanwhile, proceed with the dry ingredients.
• 3 In a separate bowl, combine cocoa powder, flour, cornstarch, baking soda, and salt. Whisk the mixture to break up any lumps. Set aside.
• 4 Whisk oil into the melted butter/sugar. Then whisk in eggs and egg yolk, followed by vanilla. Tap the whisk on the side of the bowl to remove excess batter and remove the whisk from the bowl. Sprinkle the dry ingredients over the wet ingredients and stir with a silicone spatula or wooden spoon until just a few streaks of flour remain - make sure not to overmix. Add the chocolate chips and stir until completely combined.
• 5 Add the batter to the prepared pan and smooth into an even layer. Bake the 9x9 pan for 19 minutes and the 8x8 pan for 26 minutes. The brownies should be removed from the oven when a toothpick inserted into the brownies come out with moist fudgy crumbs on it (no thin raw batter). Remember, there are chocolate chips in there, so melted chocolate is ok. Place the pan on a wire rack to cool completely. Store tightly covered at room temperature for up to 2 days, refrigerated for up to 4 days, or frozen for up to 3 months.