Preheat oven to 325°F. Line a large rimmed baking sheet with parchment paper, leaving some overhang for easy removal. Lightly spray with nonstick spray.

In a large bowl, whisk together brownie mix, water, oil, and egg white until just combined. The batter will be slightly thinner than typical brownie batter. Do not overmix.

Pour batter onto prepared sheet. Use an offset spatula to spread into an even, thin layer (about ⅛ inch thick). The thinner, the crispier. Sprinkle with mini chocolate chips, pressing lightly to adhere.

Bake for 25–30 minutes, or until the top looks set and edges are slightly firm. Rotate the pan halfway through for even crisping.

Cool the pan on a wire rack for at least 1 hour—this helps the brittle crisp up.

Once thoroughly cooled and crisp, lift the parchment and transfer the brittle to a cutting board. Use a pizza cutter for clean squares/rectangles, or break into rustic shards.