Remove corn kernels from cobs and reserve. Cut cobs into two-inch pieces. Place cob pieces into a 2-quart saucepot with the water or stock. Bring to a boil then reduce to a simmer. Simmer, covered, for 30 minutes. Strain and reserve the corn broth. Discard cobs.

Melt the butter in a large saucepot over medium heat. Add the reserved corn kernels, leek, onion and celery. Sprinkle cumin, salt, white pepper and pinch of cayenne over the vegetables. Reduce to medium-low heat and sauté until vegetables soften, about 4 minutes.

Add potatoes and strained corn stock. Simmer on medium-low heat until potatoes are tender, about 30 minutes.

Puree soup in batches in a blender or food processor until smooth. Alternately, the soup can be pureed directly in the pot with an immersion blender. Add buttermilk and parsley, stirring to combine. Cool soup to room temperature, then refrigerate. Sprinkle fresh chives on top of fi nished soup.