Bring 18cups of lightly salted water to a boil in an 8-quart covered pot over high heat.
Meanwhile, shuck the corn and, using a sharp knife, remove the kernels from the cobs, reserving the cobs and the kernels. You should have about 6cups of kernels. When the water reaches a boil, add the buttery spread and the corncobs to the water. Cover and cook at a rapid boil, stirring occasionally for 30 minutes, until the water turns a pale yellow and is fragrant. Place a large plate by the stove, and using tongs, carefully remove the corncobs from the water, then discard them. Add the reserved corn kernels and the diced potatoes. Add alittle pepper. Stir to combine. Cover and continue boiling for another 30 minutes, stirring occasionally, until the potatoes have broken down into small pieces.
Taste for seasoning. Remove from heat. Carefully ladle the soup into a blender cup to fill it only half full. (Do not fill the blender cup all the way because hot liquids expand as you blend them and you’ll get burned.) Set an empty pot by the blender. Put an oven mitt on the hand that you’ll use to cover the blender cup to protect yourself from burning your hand should any hot soup splatter the cover. Cover the blender, keeping one hand on top to hold down the cover, and blend the soup first on low speed for about 10 seconds, then on high speed for about 30 seconds until it is smooth and creamy.
Pour the blended soup into the empty pot. Continue blending the rest of the soup. Serve the soup hot, topped with alittle of the chopped bell pepper and with a spoonful of sour cream swirled in if you desire. Sprinkle with additional black pepper, if desired.