Heat butter/oil in large pot over medium heat. Add leeks and saute for 3 minutes. Stir in curry paste and cook for an additional minute.
Add corn, coconut milk and water. Simmer for 35 minutes.
Place half of soup and cilantro in blender. Puree until smooth. Transfer pureed soup into pot with remaining soup. Optionally, stir in hot sauce. I like mine a little spicy!