1. In a large heavy pot heat olive oil over medium high heat.
2. Add garlic and saute until softened, about 2 minutes.
3. Add white wine and cook for 1 minute, then add the fish broth.
4. Crush the tomatoes and add to the pot with their juices.
5. Add basil, salt and pepper then bring to a simmer and cook for 15 minutes.
6. Add the clams and mussels to the pot, cover tightly and cook until the shells open.
7. Transfer clams and mussels to serving plates, pour sauce over and serve.