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 - Submerge gelatin sheets in cold water for 5 minutes to soften. If using powdered gelatin, sprinkle over 2 tbsp cold water and let bloom.
03 - Warm 2 tbsp raspberry puree in small saucepan over low heat. Squeeze excess water from gelatin sheets and stir into warm puree until dissolved. Combine with remaining puree and cool to room temperature.
04 - Using clean bowl and beaters, whip heavy cream with vanilla extract until medium peaks form. Refrigerate until ready to use.
05 - Whisk egg whites in separate bowl 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 barely combined. Carefully fold in meringue in two additions until mixture is smooth and fully incorporated.
07 - Pipe or spoon mousse into individual serving glasses. Refrigerate minimum 2 hours until completely set.
08 - Top with fresh raspberries. Optionally dust with powdered sugar or add fresh mint leaves just before serving.