Preheat the oven to 325 degrees F. Line a heavy duty 13x18 inch baking sheet with nonstick foil or parchment paper.
In a mixing bowl, whisk the egg whites until foamy. Gradually whisk in the sugar, then whisk in the cocoa powder, oil and vanilla until smooth. Whisk in the salt and baking powder (making sure the baking powder doesn’t clump), then whisk in the nonfat milk powder. Add the flour and stir until smooth, then stir in ½ cup of the chocolate chips.
Empty batter onto the lined cookie sheet and spread as thinly as possible using the back of a spoon or scraper. Sprinkle a few more chocolate chips into areas where they did not clump together (the chips tend to congregate). Remember to try to make the bark as thin as possible.
Bake on center rack for 20 minutes. Remove from oven. With a pizza cutter or knife, cut into pieces without separating – you want shards, similar to what you’d get if making peanut brittle. Return to oven for 5 minutes.
Remove from oven and let cool completely. Pull apart. At this point, it should be completely crisp. If you are left with a few thick, chewy, pieces, return them to the oven and bake at 250 for 20 minutes, then re-cool. If your batter is thin enough the first time, you should not need the second bake.