Heat oil in a heavy 10m quart pot over medium heat.
Add onions and
garlic and saute until onions are tender, about 10 minutes. Add
tomatoes with juices and next 8 ingredients. Bring to boil. Reduce
heat and simmer uncovered until flavors blend and liquid is slightly
reduced, about 45 minutes.
Add clams to cooking liquid. Cover pot and cook
until clams open,
about 10 minutes (discard any clams that do not open). Add fish,
shrimp and scallops. Simmer until seafood is just cooked through,
about 5 minutes. Season stew to taste with salt and pepper.
Ladle stew into bowls. Sprinkle with basil. Makes 12 servings.