How to Make It
Cut the kernels from the cobs (you should have about 8 cups); reserve the cobs. Set aside 1/3 cup of the raw kernels for garnish.
In a juicer, juice 3 cups of the corn kernels. Reserve the juice.
In a large pot, combine the corn cobs and 4 quarts of water and bring to a boil. Simmer over moderate heat, occasionally skimming the foam, until the broth is reduced to 6 cups, about 1 hour. Strain the corn broth through a sieve into a large bowl; discard the cobs.
In a large saucepan, melt the butter. Add the onion and cook over moderately low heat, stirring occasionally, until softened, 10 minutes. Add the remaining corn kernels and the vadouvan and season with salt. Cook, stirring, until very fragrant and the kernels are well coated in the spices, 2 minutes. Add the corn broth and simmer over moderate heat until the liquid is reduced by half, 1 hour. Stir in the reserved corn juice.
In a blender, and working in 2 batches, puree the soup until smooth; add water if a thinner consistency is desired. Strain the soup through a sieve into a large bowl. Stir in the lime juice and season with salt. Serve warm, garnished with the reserved raw corn kernels.
Vadouvan is a French spice blend that's inspired by Indian curry. It's available at specialty food shops and from amazon.com