Preheat medium pot over medium high heat. Add olive oil, butter, onions and carrots and saute 5 minutes. Add 4 cups chicken stock, curry and cayenne, and about 1 teaspoon salt to the pot. Bring to a boil, cover and cook until carrots are very tender, about 15 minutes. Place pot on a trivet next to food processor. Process soup in 2 or 3 small batches until soup is smooth and carrots are fully pureed. Transfer processed soup into a large bowl as you work to make room for more soup in the food processor. Return completed soup to the soup pot and place back over low heat. If the soup is too thick, add remaining stock, up to 2 cups, to achieve desired consistency. Adjust seasonings. Place sour cream in a plastic condiment squeeze bottle or into a medium food storage bag. Cut a very small hole in the corner of the bag with scissors. Ladle soup into bowls and squirt a swirl of sour cream around the bowl from the center out to the rim. Drag a toothpick from the center of the bowls out to the edges, forming a spider web design on soup. Pile a few pieces of cut chives at the center of each bowl to resemble green spiders in their webs! Cool!