Whisk mayonnaise, garlic and buttermilk in small bowl until smooth. Stir in chives. Season to taste with salt and pepper. Cover and refrigerate 1 hour to allow flavors to blend.

Heat 1 tablespoon oil in heavy large Dutch oven over medium heat. Add onion and leek and saute until tender but not brown, about 10 minutes. Add wine and boil until almost all liquid evaporates, about 2 minutes. Add fish bones, water, parsley, peppercorns and bay leaf. Simmer until liquid is reduced to 6 cups, about 1 hour. Strain; discard solids.

Heat remaining 2 tablespoons oil in heavy large Dutch oven over medium high heat. Break pasta into 2 inch lengths and add to Dutch oven. saute until pasta is golden brown, about 5 minutes. Add stock. Cook until pasta is almost tender, but mixture is still soupy, about 3 minutes. Add clams, pushing into broth. Cover and cook until clams open, about 8 minutes. Discard any clams that do not open. Season to taste with salt and pepper.

Ladle into bowls. Spoon dollop of garlic mayonnaise over and serve.