1. melt butter in heavy medium skillet over medium heat. add fennel and saute until golden, about 10 minutes. add 1 cup water; cover and cook until fennel is very tender, about 20 minutes. puree fennel mixture in processor and set aside.
2. heat oil in heavy large saucepan over medium heat. add garlic and saffron; saute 1 minute. add clam juice, cream and pernod and bring to simmer. add fennel puree and bring to simmer (can be made 1 day ahead. refrigerate uncovered until cold. cover and keep refrigerated. simmer before continuing.) add oysters with their liquor to cream mixture and stir to heat through. ladle soup into bowls.