Preheat oven to 325F°

Combine flour, baking soda, salt, and cinnamon

Place 1 cup chocolate chips with butter in a large bowl (microwaveable) and zap on high it for 30 seconds. Remove the bowl from the microwave and stir. Place it back in the microwave and zap it for 15 seconds. Remove and stir. Repeat the 15-second zap & stir two more times or until chocolate and butter are melted and combined.

Stir in the cocoa powder and sugar into your melted butter & chocolate mixture.

Whisk egg whites in a small bowl and then add the vanilla and milk to whisked whites.

Whisk egg white mixture into the melted chocolate mixture. The brownie batter should be smooth.

Add remaining dry ingredients to batter and stir to combine. I found a rubber spatula worked well as the batter will be thick.

Line two 10" by 13" baking pans with parchment paper

Divide the dough between the two baking sheets.

Spread the batter to a thickness of no more than 1/4". If you have a small offset spatula, it is helpful for this. This is an important note! Naturally, you'll have more batter in the middle of the pan, try to level it out so that it is a thin layer of even thickness throughout. Why this is important: the outside edges will cook quicker than the middle. The more even the thickness, the less likely you will end up with burnt edges and a soft middle. You can see that with my 10" X 13" baking pans, the batter did not fill up the pan.

Sprinkle chocolate chips and nuts (optional) over the brownie brittle.

Bake for approximately 26 minutes, checking after 22 minutes. Touch the middle of the brownie brittle with your finger. When done, it should barely give when pushed lightly.

Remove your brittle from the oven and immediately cut it with a knife or pizza cutter, but then let it cool in the sheet pan on wire racks. The simple step of cutting it while still warm will prevent you from getting brownie brittle crumbs all over your kitchen if you snap it when it is cool.

Once completely cool, store in an airtight container.