Preheat your oven to 350°F (175°C) and grease or line two mini muffin tins (24–30 cavities).
Make the brownie batter by whisking melted butter, cocoa powder, and sugar until smooth. Mix in vanilla and eggs, then stir in flour, salt, and baking powder until just combined.
Scoop the batter into the tins, filling each about ¾ full. Bake for 14–16 minutes, until the centers are set but soft.
While still warm, press a rounded tablespoon into the center of each to make a divot. Cool completely before removing from the pan.
To make the mousse, bloom gelatin in ¼ cup cold water. Simmer raspberries, sugar, and remaining ¼ cup water for 5 minutes, then blend and strain if desired.
Stir in the bloomed gelatin and return to low heat until dissolved and slightly thickened. Let cool to room temperature.
Whip the cream to stiff peaks. Gently fold in the cooled raspberry mixture until smooth and fluffy.
Pipe or spoon the mousse into the brownie centers and chill for at least 30 minutes to set.
Before serving, drizzle with raspberry preserves or top with fresh berries.