Heat butter in a large saucepan. Add scallion, onion, ginger, curry powder, salt, and pepper. Cook over medium heat, stirring occasionally, for eight to 10 minutes, or until the vegetables have softened. Add the carrots and chicken stock. Cover and simmer for 20 minutes, or until the carrots are very soft.
Remove from the stove and cool enough to purée in a blender. Purée the carrot mixture in small batches with the coconut milk until it is very smooth. Transfer the purée to a bowl and stir in the lime juice and zest. Chill the soup for at least six hours or overnight. Serve chilled and garnished with scallions and peanuts.
This soup may be made and refrigerated up to two days in advance.