In a 2- to 3-quart pan over high heat, bring rice, cardamom, salt, and 1 1/2 cups water to a boil. Lower heat to maintain a simmer, cover, and cook until water is absorbed and rice is tender, 20 to 25 minutes. Fluff with a fork, cover, and let cool to room temperature. Discard cardamom pods.
In a bowl, combine cream, sugar, mascarpone, and rose water (if using). Whip mixture with an electric mixer at medium speed, until thickened.
Stir in rice. Spoon into eight bowls or dessert glasses. Cover and chill until cold, at least 1 hour. Just before serving, sprinkle with chopped pistachios.