Notes: Buy rosewater at Indian and Middle Eastern markets or at liquor stores.
In a blender, combine 3 cups buttermilk, cardamom seed, rosewater, and ice. Whirl until ice is finely crushed; pour into a pitcher.
Stir in remaining buttermilk, 1 1/3 cups water, and sugar and salt to taste.
Pour into glasses and garnish with mint sprigs.