Preheat the oven to 300°F (150°C). Line a baking sheet with parchment paper.

In a medium bowl, whisk together flour, cocoa powder, cornstarch, espresso powder, salt and baking soda. Set aside.

In another medium bowl, beat egg whites with sugar, vanilla extract and mint extract until foamy. Add the dry ingredients and mix until smooth. Stir in the vegetable oil. Pour the batter on the prepared baking sheet. Using an offset spatula spread the batter evenly into a thin layer (about ¼ inch thin). Sprinkle the mint chips all over the batter. Bake for 25 minutes. The brownie will be on the soft side, but it’ll harden as it cools.

Transfer the baking sheet onto a wire rack to cool completely. Break the brownie crisp into small pieces and enjoy! Store in airtight container at room temperature for up to 5 days.