1 (14 ounce) can unsweetened coconut milk (not low-fat)
1/4 cup olive oil
2 teaspoons brown mustard seeds
8 fresh curry leaves
Steps:
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.
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.
Note: Can be made up to one day in advance. I use the food processor for the chopping of onions, garlic & the immersible blending to puree the soup.