Remove leaves and strings from the corn cobs and cut them flat at the ends. Place on the surface and cut the kernels from the cob with a sharp kitchen knife. Cook two-thirds of the kernels in a little unsalted water until just tender. Set aside. Sauté remaining celery, corn kernels, carrot and shallot in butter. Sprinkle the cornmeal over the top and sauté briefly. While stirring, add the soup. Bring to a boil and reduce heat to low for about 20 minutes. Cut the leek into small pieces. Blanch in a little salted water for 1 minute. Drain, cool and put aside. Blend soup finely in a hand blender or with a hand blender, pass through a sieve if desired. Add cream, corn kernels and leek. Season with salt and pepper.