01 - Puree the raspberries with sugar and lemon juice in a blender until completely smooth. Strain through a 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 for 5 minutes.
03 - Warm 2 tbsp raspberry puree in a small saucepan over low 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 - In a clean chilled bowl, whip heavy cream with vanilla extract using hand mixer or stand mixer until medium peaks form. Refrigerate until needed.
05 - In a separate clean bowl, whisk egg whites until soft peaks form. Gradually add powdered sugar while continuing to whip until stiff, glossy peaks form.
06 - Gently fold cooled raspberry puree into whipped cream until partially combined. Carefully fold in meringue in two additions, using spatula to incorporate without deflating, until mixture is smooth and uniform.
07 - Divide mixture evenly among serving glasses or pipe into individual serving dishes. Refrigerate for at least 2 hours or until completely set.
08 - Top chilled mousse with fresh raspberries. Optionally dust with powdered sugar or add fresh mint leaves. Serve immediately.