In a large pot heat olive oil over medium-low heat. Add onion; cook until slightly softened, about 3 minutes. Add curry powder and turmeric; cook 1 minute. Add broth, the water, ginger, and, if using, corn cobs. Bring to boiling; reduce heat. Simmer, covered, 20 minutes.
Remove cobs from broth; cool slightly. Using back of a paring knife, scrape cobs over pot to remove as much liquid as possible; discard cobs.
Stir in lentils. Bring to boiling; reduce heat. Simmer, covered, 15 minutes or until lentils are tender. Season with salt and black pepper. Stir in 2 cups corn; cook 10 minutes more, stirring occasionally.
Using an immersion blender or food processor, blend soup until smooth. Just before serving, in a small saucepan heat chili oil over medium heat. Add remaining 1 cup corn to oil. Cook until corn is golden, 3 to 4 minutes. To serve, top soup with toasted corn, flowers and, if desired, sour cream.