Ingredients

1. 3 tablespoons olive oil
2. 1 large onion, chopped
3. 4 garlic cloves, crushed
4. Kosher salt, freshly ground pepper
5. 2 oil-packed anchovy fillets, chopped
6. 1 tablespoon tomato paste
7. 5 cups canned diced tomatoes, plus 1/2 cup tomato juice
8. 3 tablespoons chopped basil
9. 1/4 teaspoon red pepper flakes
10. 1/2 cup clam juice
11. 1/2 cup dry white wine
12. 12 small clams, such as Manila or littleneck, scrubbed
13. 16 mussels, scrubbed, debearded
14. 10 ounces large shrimp, peeled, deveined
15. 10 ounces bay scallops
16. 12 ounces fresh fettuccine (or 8 ounces dried)
17. 5 ounces baby spinach leaves