01 - Puree raspberries with granulated sugar and lemon juice in blender until smooth. Strain through fine mesh sieve to remove seeds completely. Set 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 for 5 minutes to bloom.
03 - Warm 2 tablespoons raspberry puree in small saucepan over low heat. Remove from heat, squeeze excess water from gelatin sheets and stir into warm puree until dissolved. For powdered gelatin, stir bloomed mixture into warm puree. Combine with remaining puree and cool to room temperature.
04 - Using hand mixer or stand mixer, whip cold heavy cream with vanilla extract in clean chilled bowl until medium peaks form. Refrigerate until ready to use.
05 - In separate clean bowl, whisk egg whites to soft peaks. Gradually add powdered sugar while continuing to whip until stiff, glossy peaks form.
06 - Fold cooled raspberry puree into whipped cream until partially incorporated. Gently fold in meringue until mixture is smooth and uniformly colored, taking care not to deflate.
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.