Put 1/4 cup water in a small bowl and sprinkle the gelatin on top. Set aside.
In a medium sized bowl, mash the raspberries and then strain into another bowl to remove seeds. This should give you about 1 2/3 cups of raspberry puree. Add sugar and lemon juice, then stir together until all the sugar dissolves.
Microwave the softened gelatin for 30 seconds. Measure 1/4 cup raspberry puree and set aside. Whisk gelatin into remaining raspberry puree.
Whip the heavy cream until stiff. Fold in 1/3 of raspberry-gelatin until nearly incorporated. Fold in remaining raspberry mixture in 2 more batches in the same manner. Drizzle reserved raspberry puree onto mousse and fold once or twice.
Put mousse in a glass bowl, cover and refrigerate until set; about 2-3 hours. Serve in individual glass bowls or dishes or chocolate cups.