01 - Puree raspberries with 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 bloom for 5 minutes.
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 clean bowl, whip cold heavy cream with vanilla extract using hand mixer or stand mixer until medium peaks form. Refrigerate whipped cream until needed.
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 until nearly incorporated. Carefully fold in meringue in two additions, using spatula to maintain airiness until mixture is smooth and uniform.
07 - Divide mousse evenly among serving glasses or pipe using pastry bag. Refrigerate for minimum 2 hours or until completely set and firm.
08 - Top each portion with fresh raspberries. Optionally dust with powdered sugar or add fresh mint leaves. Serve chilled.