In a small bowl, combine the raspberries, granulated sugar, and lemon juice. Mash the raspberries lightly with a fork and set aside to macerate for about 10 minutes.
In a separate bowl, sprinkle the gelatin over the cold water and let it sit for about 5 minutes until it blooms. Then, gently heat the mixture in the microwave for about 10-15 seconds until the gelatin dissolves completely. Allow it to cool slightly.
In a large mixing bowl, whip the heavy cream, powdered sugar, and vanilla extract until soft peaks form.
Carefully fold in the raspberry mixture and the dissolved gelatin until well combined.
Spoon the mousse into serving dishes and refrigerate for at least 2 hours to set.
Before serving, top with additional fresh raspberries for garnish.