Pistachio Soup

Ingredients

• ["3/4 cup unsalted shelled pistachio (4 oz, not dyed red)", "2 cups reduced-sodium chicken broth (16 fl. Oz)", "1 medium leek (white and pale green parts only)", "1/4 cup finely chopped onion", "1 garlic clove, finely chopped", "1/4 teaspoon finely grated peeled fresh ginger", "1/8 teaspoon cayenne", "1 1/2 tablespoons vegetable oil", "1 tablespoon cumin seed", "1/2 teaspoon coriander seed", "2 cups water", "3/4 teaspoon salt", "1/2 teaspoon black pepper", "1/8 teaspoon turmeric", "2 tablespoons rice flour", "2 tablespoons dried barberries (aka \"zereshk\""... you can substitute cranberries soaked first in hot water)""