Shuck cobs and with a sharp knife carefully cut kernels from cobs, then use back of knife to run across cob to scrape the cob's milk into kernels. Divide kernels into two 3-cup batches and reserve cobs.
To prepare soup base: In a large pot over high heat, bring salted water to a boil. Add diced potatoes and blanch for 6 to 8 minutes, until potatoes are just tender enough to be pierced by a fork. Plunge potatoes into ice water, drain and reserve.
In a large stock pot over medium heat, warm olive oil. Add onions and cook until soft, stirring occasionally. Add russet potatoes and cook for about 3 minutes. Add 3 cups roasted corn kernels, corn cobs, garlic, ginger and turmeric. Cook, stirring occasionally, until corn kernels get soft, about 5 minutes.
Add wine, bring to a simmer and reduce liquid by half. Add 3 quarts water and clam juice, bring to a simmer and cook until potatoes become very soft, at least 45 minutes and up to an hour. ("This is very important," said Becht. "For the texture of the soup to be correct, it must be really, really velvety-tasting. If you purée the soup too soon, it will have a grit to it and this is not desirable. Be patient.")
When potatoes and corn kernels are very soft, remove corn cobs and, working in batches, using a blender on high speed, purée soup, adding enough cream to each batch to use entire cup. Pass puréed soup through a fine-mesh sieve. ("At this point, you should have a soup that is a brilliant yellow color and will coat a spoon," said Becht. "Keep in mind that it will thicken quite a bit as it cools; only practice will tell how much, but for now, just don't worry too much if it seems somewhat thin, it will change.")
Transfer soup to a covered container and refrigerate until cool, at least 1 hour.