Combine tomatoes, basil, sugar, and 2 tablespoons salt in a pot. Simmer, covered, over low heat for 45 minutes.

Strain tomato mixture, pressing on solids to capture liquid.

Cook onion, celery, carrot, garlic, olive oil, and remaining 1/2 teaspoon salt in a heavy-bottomed pot for 15 minutes, until softened.

Add strained tomato mixture and simmer for 10 minutes, until thickened.

Blend soup until smooth, adding vegetable stock to thin if needed.

In a separate pot, combine clams and white wine. Bring to a simmer.

Add mussels and cook until they open.

Add shrimp and cook until pink and opaque.

For saffron cream, sauté garlic in a pan. Add saffron and cream, and simmer until slightly thickened.

Serve soup with seafood and a drizzle of saffron cream.