Heat a large, heavy bottomed pot over medium heat. Add butter and oil and swirl to coat the bottom of the pan.
Add the corn kernels along with the salt, white pepper and thyme. Cook corn kernels for about ten minutes, stirring frequently, until the kernels just begin to color. Watch your heat and don't let them burn.
Stir in the corn stock, heavy cream and crème fraiche. Bring to a boil, then reduce heat and simmer, uncovered, for about 30 minutes. If using sour cream, add it now--you don't want sour cream to boil, or it will curdle. Taste and adjust seasonings. Add a few drops of hot sauce, if you'd like.
Remove from the heat and carefully blend in batches until smooth. When pureeing hot foods in a blender, be sure to only fill the blender jar halfway and to remove the center feed tube to let heat escape. Start the blender on low speed first, then increase to high.
You can also blend this right in the pan with an immersion blender. Check the consistency. If you'd like it a little thicker, continue to simmer until it has reached your desired consistency. If you think it is too thick, thin it out with a little broth, water or even some more cream.
Strain soup through a fine strainer and serve hot, garnished with a dollop of sour cream or crÃ¨me fraiche and some freshly minced herbs.
To make a lower-fat version, stir in 3 tablespoons of corn starch or flour along with another tablespoon of oil after you've cooked the corn for about eight minutes. Stir well and continue to cook for another minute or two before adding the corn stock or vegetable stock.
Use 2 cups whole milk in place of the heavy cream and crème fraiche.