Preheat oven to 350 F. Grease an 8-inch square baking dish. Set aside.
Melt butter in a large, heavy saucepan over low heat.
½ cup butter
Stir in cocoa powder until well-combined.
¼ cup unsweetened cocoa powder
Remove from heat, and stir in sugars and vanilla.
½ cup light brown sugar, ½ cup granulated sugar, 1 teaspoon vanilla
Add eggs, and stir in.
2 large eggs
Stir in cornstarch and salt.
¼ cup cornstarch, ½ teaspoon salt
Fold in chocolate chips.
½ cup mini semisweet chocolate chips¹
Pour into prepared baking dish and smooth top with a spatula.
Bake until edges are firm and center is just set, about 25-30 minutes. A toothpick inserted in the center should come out with fudgy crumbs attached. Do not overbake.
Let cool in pan to room temperature.
Place, uncovered, in freezer for at least 1 hour before cutting and serving.
Notes
Can sub regular chocolate chips.
If you need the brownies to be gluten-free, be sure to check the labels on your ingredients to ensure that they are gluten-free.