Puree the raspberries in a food processor, cover, and blend until smooth. Strain to remove the seeds and transfer the puree to a large bowl. Stir in the sugar and lemon juice.

Sprinkle the gelatin over cold water in a small saucepan and let sit for 1 minute. Stir over low heat until the gelatin has completely dissolved. Pour this into the raspberry mixture and stir to combine. Refrigerate for about 1 hour until it thickens slightly.

Transfer the thickened raspberry mixture to a large bowl. Beat on high speed until foamy, about 1 minute. Gradually add the whipping cream and continue beating until the mixture thickens to mousse consistency, approximately 2 minutes.

Spoon the mousse into dessert bowls or glasses. Cover and refrigerate for 1–2 hours until set. If desired, garnish with fresh mint leaves and extra raspberries.