Cocoa Bark :
(from Chewy Gooey Crispy Crunchy by Alice Medrich)
4 tablespoons butter, melted and still very warm
20g natural (non-alkalized) cocoa powder, sieved after measuring
1/8 teaspoon salt
2 large egg whites
1 tablespoon plus 1 teaspoon plain flour
Preheat the oven to 175′C. In a small bowl, whisk together the melted butter, sugar, cocoa and salt. Whisk in the egg whites. Add the flour and whisk only until combined. Let rest for at least 10 minutes or cover and refrigerate for up to 3 days.
To bake, use an offset spatula to spread half the batter onto each of two cookie sheets lined with silicone mats. Each sheet of batter should be about 9 by 13 inches wide and less than 1/8 inch thick. [Sprinkle each sheet with your topping of choice. I used crushed potato chips and grated cheese. You can even use nuts,crushed peppermint candies, or whatever you may desire.
Bake each sheet for 11 to 13 minutes until the batter turns a faintly darker shade of brown. Rotate the pan from back to front halfway through the baking time to ensure even baking. Cool completely on a rack before breaking the cookie into random shards.