Preheat oven to 350°F (175°C). Grease an 8x8 inch square baking pan and line with parchment paper.

In a medium bowl, whisk melted butter and sugar. Add eggs and vanilla, whisking until smooth.

Sift in cocoa powder, flour, salt, and baking powder. Fold gently until just combined.

Pour into the pan and bake for 20-25 minutes. Let cool completely.

Use a heart-shaped cookie cutter to cut out 8 brownie hearts.

In a small saucepan, combine raspberries, 1/4 cup sugar, and lemon juice. Cook over medium heat until berries break down.

Press the mixture through a fine-mesh sieve to remove seeds. You should have about 3/4 cup of smooth puree.

In a small bowl, sprinkle gelatin over 2 tbsp cold water. Let it bloom for 5 minutes, then microwave for 10 seconds until melted.

Stir the melted gelatin into the warm raspberry puree and let it cool to room temperature.

In a large chilled bowl, whip heavy cream and powdered sugar until stiff peaks form.

Gently fold the cooled raspberry puree into the whipped cream until the color is uniform and the mixture is light and airy.

Place the brownie hearts into heart-shaped silicone molds or keep them on a tray with heart-shaped rings around them.

Pipe or spoon the raspberry mousse over each brownie heart, smoothing the tops.

Refrigerate for at least 4 hours, or until the mousse is completely set.

Carefully unmold the hearts.

Garnish with a fresh raspberry on top and a sprinkle of dark chocolate shavings.

Serve chilled for the best texture and flavor.