Preheat your oven to 350°F (175°C). Grease an 8-inch round cake pan and line the bottom with parchment paper. Prepare the gluten-free brownie mix according to the package instructions, pour the batter into the pan, and bake for 20–25 minutes until a toothpick comes out with a few moist crumbs. Allow the brownie base to cool completely in the pan.

While the brownie cools, rinse 1 cup of fresh raspberries under cold water and drain them well. Blend the raspberries in a food processor until smooth, then strain the puree through a fine mesh sieve to remove the seeds, collecting it in a bowl. Set aside about 2 tablespoons of the smooth puree for decorating later.

Next, melt 8 ounces of good-quality dark chocolate in a heatproof bowl set over simmering water or in the microwave, stirring until smooth. Allow the melted chocolate to cool slightly. In a separate bowl, whip 2 cups of heavy cream until soft peaks form. Gradually fold the whipped cream into the melted chocolate until well combined, then gently incorporate the raspberry puree.

Once the mousse mixture is ready, pour it over the cooled brownie base in the cake pan. Cover the pan with plastic wrap and refrigerate for at least 4 hours.

After chilling, carefully remove the cake from the pan. Transfer it to a serving plate and garnish with the reserved raspberry puree, fresh raspberries, and chocolate curls. Slice into wedges and serve immediately.