01 - Puree raspberries with granulated sugar and lemon juice in a blender until completely smooth. Strain through a fine mesh sieve to remove all seeds, pressing firmly to extract maximum liquid. Set puree aside.
02 - Submerge gelatin sheets in cold water for 5 minutes until softened. Alternatively, sprinkle powdered gelatin over 2 tbsp cold water and let stand until absorbed.
03 - Warm 2 tbsp raspberry puree in a small saucepan over low heat until just warm to touch. Drain gelatin sheets thoroughly and stir into warm puree until completely dissolved. For powdered gelatin, stir bloomed mixture until fully dissolved. Combine with remaining puree and cool to room temperature.
04 - In a chilled bowl, whip heavy cream with vanilla extract using hand mixer or stand mixer until medium peaks form. Cream should hold shape but still be slightly soft. Refrigerate until ready to use.
05 - In a separate clean bowl, beat egg whites with whisk or mixer until soft peaks form. Gradually add powdered sugar while continuing to whip until stiff, glossy peaks form. Meringue should stand upright when beaters are lifted.
06 - Gently fold cooled raspberry puree into whipped cream using spatula, mixing until almost incorporated with some streaks remaining. Lightly fold in prepared meringue in two additions, using careful folding motions to maintain airiness until no white streaks remain.
07 - Spoon or pipe mousse mixture into individual serving glasses or bowls, filling nearly to top. Tap glasses lightly on counter to release air bubbles. Refrigerate for at least 2 hours or until completely set and firm to touch.
08 - Garnish chilled mousse with fresh raspberries arranged attractively on top. Optionally dust with powdered sugar or add fresh mint leaves. Serve immediately while cold.