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

Instructions

1. Cook onions in butter in a wide 6-quart heavy pot over moderately low heat, stirring occasionally, until softened, 3 to 5 minutes. Add garlic and ginger and cook, stirring, 1 minute. Add cumin, coriander, and cardamom and cook, stirring, 1 minute. Stir in salt, red pepper flakes, pumpkin, water, broth, and coconut milk and simmer, uncovered, stirring occasionally, 30 minutes. Purée soup in batches in a blender until smooth (use caution when blending hot liquids), transferring to a large bowl, and return soup to pot. Keep soup warm over low heat.
2. Heat oil in a small heavy skillet over moderately high heat until hot but not smoking, then cook mustard seeds until they begin to pop, about 15 seconds. Add curry leaves and cook 5 seconds, then pour mixture into pumpkin soup. Stir until combined well and season soup with salt. Soup can be thinned with additional water.