Preheat your oven to 350°F (175°C) and line a 9x13 inch pan with parchment paper for easy removal later. Use a bit of butter to stick the paper in place.

In a large mixing bowl, whisk together the melted butter, granulated sugar, brown sugar, eggs, and vanilla extract until well combined and fluffy, about 2-3 minutes. The mixture should be glossy.

Gently fold in the flour, cocoa powder, and salt using a spatula. Just combine until you don’t see any flour streaks; overmixing can lead to tough brownies.

Pour the batter into the prepared baking pan, spreading it evenly. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs. The edges should look set, while the center remains slightly soft.

While the brownies are cooling, heat the heavy cream in a small saucepan over medium heat until it begins to simmer.

Remove from heat, add chopped chocolate, and stir until smooth. Let it cool slightly before folding in whipped cream for a lighter texture.

Once the brownies are completely cooled (or slightly warm for a more gooey effect), pour the chocolate mousse over the brownie layer, smoothing it out with a spatula.

Refrigerate for at least 1 hour to set.

When ready to serve, slice the brownies into squares and enjoy the beautiful layers of brown and black against each other. Top with chocolate shavings or a dusting of cocoa powder for added flair.