Curried Pumpkin Soup

Name: Curried Pumpkin Soup
Ingredients: 2 medium onions, finely chopped (2 cups); 2 tablespoons unsalted butter; 2 large garlic cloves, minced; 1 1/2 tablespoons minced peeled fresh ginger; 2 teaspoons ground cumin; 1 teaspoon ground coriander; 1/8 teaspoon ground cardamom; 1 1/2 teaspoons salt; 3/4 teaspoon dried hot red pepper flakes; 2 (15-oz) cans solid-pack pumpkin (3 1/2 cups; not pie filling); 4 cups water; 1 1/2 cups reduced-sodium chicken broth (12 fl oz); 1 (14-oz) can unsweetened coconut milk (not low-fat); 1/4 cup olive oil; 2 teaspoons brown mustard seeds; 8 fresh curry leaves