Creating Chocolate Mousse Brownies is simple if you follow these clear steps:

Brownie Layer

1. Preheat Oven: Preheat your oven to 350°F (175°C). Grease a 9×13-inch baking pan.
2. Melt Butter: In a saucepan over low heat, melt the unsalted butter. Remove from heat and let it cool slightly.
3. Mix Ingredients: In a large bowl, combine the melted butter and granulated sugar. Mix well.
4. Add Eggs and Vanilla: Whisk in the eggs, one at a time, followed by the vanilla extract.
5. Combine Dry Ingredients: In another bowl, sift together the flour, cocoa powder, salt, and baking powder.
6. Combine Mixtures: Gradually add the dry ingredients to the wet mixture, stirring until just combined.
7. Pour Batter: Spread the brownie batter evenly in the prepared baking pan.
8. Bake Brownies: Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.
9. Cool Brownies: Remove from the oven and let the brownies cool in the pan on a wire rack.

Chocolate Mousse Layer

10. Melt Chocolate: In a microwave-safe bowl, melt the chopped semi-sweet chocolate in 30-second intervals, stirring in between until smooth. Let it cool slightly.
11. Whip Cream: In a mixing bowl, whip the heavy cream until soft peaks form. Set aside.
12. Beat Eggs and Sugar: In another bowl, whisk the eggs and granulated sugar until light and fluffy.
13. Combine Chocolate and Eggs: Slowly fold the melted chocolate into the egg mixture until well combined.
14. Fold in Whipped Cream: Gently fold the whipped cream into the chocolate mixture. Be careful not to deflate the mousse.
15. Spread Mousse: Once the brownies are completely cool, spread the chocolate mousse evenly over the brownie layer.
16. Chill: Refrigerate the brownies for at least 2 hours to allow the mousse to set.