Directions

Preheat oven to 350°F. Spray a 9-inch x 13-inch pan with nonstick cooking spray.

Whisk the cocoa and boiling water together in a large bowl until smooth. Add the unsweetened chocolate and whisk until the chocolate is melted. Whisk in the melted butter and oil. The mixture may look curdled at this point.

Add the eggs, egg yolks and vanilla. Continue to whisk until smooth. Whisk in the sugar until fully incorporated. Using a rubber spatula, fold in the flour, salt, and chocolate chips all at once, taking care to not over mix.

Scrape the batter into the prepared pan and bake until a toothpick inserted in center comes out with a few moist crumbs attached, about 30-40 minutes. Do not overcook. Transfer the pan to a wire rack and let cool completely, about 1-1 1/2 hours. Cut when cooled.