• Preheat the oven to 350°F (175°C). Grease or line an 8×8-inch baking pan with parchment paper.

• In a large bowl, whisk together the melted butter and sugar until smooth. Add eggs, one at a time, beating well after each. Stir in vanilla extract.

• In a separate bowl, whisk together cocoa powder, flour, salt, and baking powder. Gradually fold the dry ingredients into the wet mixture until well combined. The batter will be thick.

• Pour the batter into the prepared pan and bake for 18-22 minutes, or until a toothpick inserted comes out with just a few moist crumbs. Let the brownies cool completely.

For the chocolate mousse:

• Heat heavy cream in a saucepan over medium heat until it begins to simmer (do not boil).

• Pour the hot cream over chopped chocolate in a heatproof bowl. Let it sit for 2-3 minutes, then stir until smooth.

• Once the chocolate mixture is cool, whip the remaining heavy cream until soft peaks form. Gently fold the whipped cream into the chocolate mixture until it becomes light and fluffy.

Assemble the brownies:

• Once the brownies have cooled, spread the mousse evenly over the brownie layer. Smooth it out with a spatula.

• Refrigerate the brownies for 2-3 hours, or until the mousse sets.

Serve:

• Once chilled, slice into squares. Optionally, garnish with chocolate shavings, whipped cream, or berries. Serve and enjoy!