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 for later use.
02 - Submerge gelatin sheets in cold water for 5 minutes to soften. If using powdered gelatin, sprinkle over 2 tbsp cold water and let stand until absorbed.
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. For powdered gelatin, stir bloomed mixture until fully dissolved. Combine with remaining puree and cool to room temperature.
04 - In chilled bowl, beat heavy cream with vanilla extract using hand mixer or stand mixer 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 - Gently fold cooled raspberry puree into whipped cream using spatula until mostly incorporated. Carefully fold in meringue in two additions until mixture is smooth and uniform, taking care not to deflate the airy texture.
07 - Transfer mousse to piping bag or spoon directly into individual serving glasses. Refrigerate for minimum 2 hours until completely set and firm.
08 - Garnish chilled mousse with fresh raspberries. Optionally dust with powdered sugar or add fresh mint leaves just before serving.