In saute pan heat olive oil and cook onions until transparent. Add corn and cook until very tender, about 7 10 minutes. Set aside. Slice cobs. Place cob slices in a sauce pan and cover with water. Bring to a boil and add spice bag. Let simmer until you have 2 cups of liquid. Strain broth and discard cobs and spice bag. Add broth to onions and corn mixture. Let simmer for about 5 minutes and then place in a food processor. Process until smooth. Pass through a strainer and season with salt, pepper and cayenne to taste. Whisk in butter. Set aside and keep warm.
* Spice Bag: half bay leaf, 1 sprig of thyme, 10 white peppercorns, 5 parsley stems placed together in tied cheesecloth