Prepare Raspberry Puree: Lightly heat raspberries with granulated sugar in a saucepan. Stir until softened, purée, and strain to remove seeds.

Optional Gelatin Preparation: If desiring firmness, sprinkle gelatin over cold water in a small bowl. Let bloom for about 5 minutes, then melt gently.

Whip Cream: In a chilled mixing bowl, beat heavy whipping cream and powdered sugar until stiff peaks form; do not over-whip.

Combine Ingredients: Gently fold the raspberry puree and vanilla extract into the whipped cream in three stages.

Cool and Set: Spoon mousse into serving dishes and chill in the refrigerator for at least 2 hours. Garnish with fresh raspberries before serving.