01 - Puree raspberries with granulated sugar and lemon juice in blender until completely smooth. Strain through fine mesh sieve to remove all seeds. Set puree aside.
02 - Submerge gelatin sheets in cold water for 5 minutes to soften. If using powdered gelatin, sprinkle over 2 tablespoons cold water and let stand until absorbed.
03 - Warm 2 tablespoons raspberry puree in small saucepan over low heat. Squeeze excess water from gelatin sheets and stir into warm puree until dissolved. Pour mixture back into remaining puree and let cool to room temperature.
04 - Whip cold heavy cream with vanilla extract in clean bowl until medium peaks form. Transfer to refrigerator until needed.
05 - Whisk egg whites in separate bowl until soft peaks form. Gradually add powdered sugar while whipping until stiff, glossy peaks achieved.
06 - Fold cooled raspberry puree into whipped cream until mostly combined. Gently fold in meringue until mixture is smooth, uniform, and no white streaks remain.
07 - Spoon or pipe mousse into individual serving glasses. Refrigerate for minimum 2 hours until completely set and firm.
08 - Top each serving with fresh raspberries. Optionally dust with powdered sugar or add fresh mint leaves just before serving.