01 -
Preheat the oven to 350°F (175°C). Grease a 9×13 inch baking pan with butter or nonstick spray.
02 -
Melt unsalted butter in a medium saucepan over medium heat. Once melted, stir in granulated sugar until thoroughly blended.
03 -
Remove the pan from the heat and let cool briefly. Whisk in eggs and vanilla extract until the mixture is smooth and glossy.
04 -
In a separate bowl, sift together all-purpose flour, unsweetened cocoa powder, salt, and baking powder.
05 -
Gradually add the dry ingredients to the butter mixture, stirring until just incorporated. Avoid overmixing to preserve tenderness.
06 -
Spread the brownie batter evenly into the prepared baking pan using a spatula.
07 -
Place the pan in the oven and bake for 30–35 minutes, or until a toothpick inserted in the center emerges with a few moist crumbs.
08 -
Remove brownies from the oven and allow them to cool completely in the pan before proceeding.
09 -
In a heatproof bowl, gently melt the semi-sweet chocolate over a double boiler or in short microwave bursts, stirring until smooth. Let cool to room temperature.
10 -
In a large mixing bowl, whip the heavy cream until it forms soft peaks.
11 -
Using a separate bowl, beat egg whites until foamy. Gradually add granulated sugar and continue beating until stiff peaks are achieved.
12 -
Fold the cooled melted chocolate into the whipped cream until well integrated. Carefully fold in the whipped egg whites, taking care not to deflate the mixture.
13 -
Spread the chocolate mousse evenly over the cooled brownie layer. Cover and refrigerate for at least 1–2 hours to set before serving.