In a small bowl, sprinkle the gelatin powder over the cold water and let it sit for 5 minutes to bloom.

While the gelatin blooms, combine the raspberries, sugar, lemon juice, and ground cardamom in a small saucepan over medium heat. Cook for about 5-7 minutes, breaking up the berries with a spoon, until the fruit breaks down and becomes saucy.

Remove the saucepan from heat. Pour the mixture through a fine-mesh sieve into a bowl to remove the seeds, pressing down with a spatula to extract as much liquid as possible.

While the raspberry puree is still hot, add the bloomed gelatin and stir vigorously until completely dissolved. Stir in the rose water. Let the mixture cool to room temperature (about 15 minutes) but do not let it set completely.

In a separate chilled bowl, whip the heavy cream until stiff peaks form.

Gently fold one-third of the whipped cream into the cooled raspberry mixture to lighten it. Then, carefully fold in the remaining whipped cream until no white streaks remain, being careful not to deflate the air.

Spoon or pipe the mousse into serving glasses. Refrigerate for at least 2 hours to set.

Before serving, garnish with fresh raspberries and a sprinkle of chopped pistachios.