- Preheat oven to 350ºF and lightly grease an 8×8 baking pan with butter or cooking spray. In a small bowl, stir together cacao powder and cornstarch.
- Melt butter and 1 cup of chocolate chips in a microwave safe bowl, stirring occasionally until smooth.
- Use a hand mixer or standing mixer to beat eggs on high speed for 1 minute, until pale yellow.
- Add brown sugar to eggs and beat 1 minute longer. Add melted butter and chocolate mixture, vanilla extract, and soy sauce (regular or gluten-free). Beat until just combined.
- Gradually beat cacao powder mixture into wet ingredients until moist. Spread batter evenly in prepared pan. Sprinkle with remaining chocolate chips.
- Bake for 20-25 minutes. Cool brownies completely at room temperature before slicing. Brownies will firm as they cool.