In a large pot, cover sweet potatoes with water, bring to boil and lower heat. Simmer until tender about 6 minutes, drain and reserve.

In large pot over medium heat, saute onion, garlic and ginger in butter until onions are transparent. Add sweet potato, coconut milk and water, and stock. Simmer for 20 minutes.

In batches, puree or blend soup until smooth or to desired texture. Add 1/2 cup of milk or stock per load in blender to desired taste/texture. Add spices and lime juice and serve.