01 -
Preheat oven to 350°F (175°C). Grease a 9×13 inch (23×33 cm) baking pan.
02 -
In a medium saucepan over medium heat, melt the butter. Remove from heat and stir in granulated sugar until thoroughly combined.
03 -
Allow the butter-sugar mixture to cool slightly. Whisk in eggs one at a time, then add vanilla extract until smooth.
04 -
In a separate bowl, sift together flour, cocoa powder, salt, and baking powder.
05 -
Gradually add dry ingredients to wet mixture, stirring gently to avoid overmixing until just combined.
06 -
Pour batter evenly into prepared pan. Bake for 30-35 minutes or until a toothpick inserted in the center comes out with moist crumbs.
07 -
Remove from oven and allow brownies to cool completely in the pan before proceeding.
08 -
Melt chopped semi-sweet chocolate in a heatproof bowl over a double boiler or microwave, stirring until smooth. Let cool slightly.
09 -
Whip heavy cream until soft peaks form using a mixer or whisk.
10 -
Beat egg whites until foamy. Gradually add granulated sugar and continue beating until stiff peaks develop.
11 -
Fold melted chocolate gently into whipped cream. Then fold in beaten egg whites carefully to retain volume.
12 -
Spread chocolate mousse evenly over cooled brownies. Cover and refrigerate for 1-2 hours to set.