For the Brownie Base:

1. Preheat your oven to 350°F (175°C). Grease and line a heart-shaped cake pan or use heart-shaped silicone molds.
2. In a mixing bowl, combine the melted butter, sugar, and brown sugar. Stir in the eggs and vanilla extract.
3. In a separate bowl, whisk together the flour, cocoa powder, baking powder, and salt. Gradually add the dry ingredients to the wet mixture until fully combined.
4. Pour the brownie batter into the prepared pan and spread it evenly.
5. Bake for 12-15 minutes or until a toothpick inserted into the center comes out clean. Allow the brownies to cool completely before removing them from the pan.

For the Raspberry Mousse:

1. In a small bowl, sprinkle the gelatin over the cold water and let it bloom for 5 minutes.
2. In a saucepan, combine the raspberries, sugar, and lemon juice over medium heat. Stir occasionally until the raspberries break down and the mixture thickens slightly, about 5-7 minutes.
3. Remove from heat and strain the raspberry mixture to remove the seeds.
4. Stir the bloomed gelatin into the hot raspberry mixture and mix until dissolved. Let it cool to room temperature.
5. In a separate bowl, whip the heavy cream to soft peaks.
6. Once the raspberry mixture has cooled, gently fold in the whipped cream until smooth.
7. Melt the white chocolate and fold it into the raspberry mousse mixture.
8. Spoon the mousse over the cooled brownie base, smoothing the top with a spatula.
9. Refrigerate for at least 4 hours, or overnight, to set the mousse.

For Decoration:

1. Once set, carefully remove the mousse from the mold.
2. Decorate with fresh raspberries on top and chocolate curls or shavings for an extra touch of elegance.