Step 1

Preheat oven to 350 degrees F. Arrange rack to lower center. I highly recommend using an inexpensive oven thermometer* to check your oven temperature. Most ovens are not preheated to the correct temperature.

Step 2

Grease and Line a 13" x 9" x 2" light colored metal baking pan* with 2 layers or parchment or foil. Overhang the parchment or foil on the long sides of the pan so you can easily lift out the whole slab of brownies once cool for easy cutting.

Step 3

Melt butter and unsweetened chocolate in a saucepan over very low heat - stirring until just melted. Turn off heat. (You can alternatively melt in the microwave using 30 second increments and stirring in-between.)

Step 4

In bowl of stand mixer, combine eggs, egg yolk, sugar, vanilla, instant espresso. Use wire whip accessory to whip for 4-6 minutes* (I start on low speed until combined, then whip on speed 8). The mixture should be transformed to very light color yellow and should be fluffy and increased 2-3x in volume.

Step 5

While, mixture is whipping, Sift flour and cocoa into a separate bowl.

Step 6

After whipping, turn mixer to low speed and drizzle in slightly cooled chocolate/butter mixture.

Step 7

Then, add in sifted flour and cocoa mixture, continue mixing on low speed, just until partly combined. Remove bowl, sprinkle chocolate chips over mixture and fold by hand gently until all the dry mixture is mixed in. Take care not to over-mix - you don't want to deflate all the air you whipped in.

Step 8

Pour into prepared baking pan and bake for about 25- 30 minutes. (start checking at 25 minutes.) When finished baking, top will be shiny and evenly puffed. Edges will look set and may start pulling away from the sides of the pan. A toothpick inserted in the center will still have some moist brownie crumbs on it. Remove to a cooling rack. Cool 20-30 minutes in pan, then use parchment/foil to remove to cooling rack. Fully cool before cutting and enjoying. (They cut more cleanly when they are cool and it gives the crumb/texture time to fully settle.)