In a saucepan over medium heat, cook raspberries, granulated sugar, and lemon juice for 5-7 minutes until broken down and syrupy.

Strain the mixture through a fine-mesh sieve into a bowl, pressing to extract juice. Discard seeds.

Place the smooth raspberry puree in the refrigerator until completely cold.

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

Gently fold the chilled raspberry puree into the whipped cream using a rubber spatula until no white streaks remain.

Pipe or spoon the mousse into individual serving glasses.

Chill in the refrigerator for at least 2 hours to set.

Garnish with fresh raspberries and a sprig of mint just before serving.