In large pot, combine broth, water, wine, apples, carrots, onion, fennel, bay leaf, thyme and peppercorns; bring to boil. Reduce heat and simmer, covered, 20 minutes. Strain soup, reserving liquid. Remove bay leaf from apple-vegetable mixture in strainer. In blender or food processor, puree mixture; add reserved liquid and blend well. Reheat soup, if necessary, ladle into soup bowls and serve with a dollop of yogurt if desired.