Creating Chocolate Mousse Brownies is a straightforward process if you follow these simple steps:

1. Preheat Oven: Preheat your oven to 350°F (175°C) and grease a 9×13 inch baking dish.
2. Melt Butter: In a saucepan over low heat, melt the butter. Remove from heat and stir in granulated sugar and cocoa powder.
3. Combine Ingredients: Add the eggs one at a time, mixing well after each addition. Stir in vanilla extract.
4. Add Dry Ingredients: Gradually add the flour and salt, stirring until just combined.
5. Bake the Brownies: Pour the brownie batter into the prepared baking dish. Bake for 25-30 minutes or until a toothpick inserted comes out with a few moist crumbs.
6. Cool Brownies: Remove from the oven and allow the brownies to cool completely in the dish.
7. Prepare the Mousse: In a separate bowl, heat the heavy cream just until it begins to simmer. Pour over the chopped chocolate and let sit for 2 minutes. Stir until smooth.
8. Whip the Cream: In another bowl, whip the remaining heavy cream until soft peaks form. Gently fold the whipped cream into the chocolate mixture until well combined.
9. Top the Brownies: Once brownies are completely cooled, spread the chocolate mousse evenly over the top.
10. Chill: Refrigerate the brownies for at least 1 hour to allow the mousse to set.
11. Serve and Enjoy: Before serving, dust with powdered sugar for an elegant touch.

Following these steps will ensure that your Chocolate Mousse Brownies are a delightful success!