01 - Puree raspberries with sugar and lemon juice in blender until completely smooth. Strain through fine mesh sieve to remove all seeds. Set aside.
02 - Soak gelatin sheets in cold water for 5 minutes. If using powdered gelatin, sprinkle over 2 tbsp cold water and let bloom.
03 - Gently heat 2 tbsp raspberry puree in small saucepan until just warm. Squeeze excess water from gelatin sheets and stir into warm puree until dissolved. For powdered gelatin, stir bloomed mixture until fully dissolved. Combine with remaining puree and cool to room temperature.
04 - In clean bowl, whip heavy cream with vanilla extract until medium peaks form. Refrigerate until ready to use.
05 - In separate bowl, whisk egg whites to soft peaks. Gradually add powdered sugar while continuing to whip until stiff, glossy peaks form.
06 - Gently fold raspberry puree into whipped cream until almost incorporated. Carefully fold in meringue in two additions until mixture is smooth and fully combined.
07 - Spoon or pipe mousse into individual serving glasses. Refrigerate for minimum 2 hours until completely set.
08 - Top with fresh raspberries. Optionally dust with powdered sugar or add fresh mint leaves. Serve chilled.