Preparation Melt butter in heavy large saucepan over medium heat. Add leeks. Cover and cook until leeks begin to soften, stirring occasionally, about 3 minutes. Add potatoes; stir 1 minute. Add clam juice and thyme; bring to boil. Cover pan, reduce heat to medium-low and simmer 6 minutes. Add cream; return to simmer. Add haddock and simmer uncovered until potatoes are tender and haddock is opaque in center, about 5 minutes. Season soup with salt and pepper. Ladle soup into bowls.
Preparation Melt butter in heavy large saucepan over medium heat. Add leeks. Cover and cook until leeks begin to soften, stirring occasionally, about 3 minutes. Add potatoes; stir 1 minute. Add clam juice and thyme; bring to boil. Cover pan, reduce heat to medium-low and simmer 6 minutes. Add cream; return to simmer. Add haddock and simmer uncovered until potatoes are tender and haddock is opaque in center, about 5 minutes. Season soup with salt and pepper. Ladle soup into bowls.