Rinse the mussels under cold running water while scrubbing the shells to remove debris. Pull away any beards and discard any shells that are cracked or remain open when tapped.

Heat olive oil and butter in a large pot over medium heat. Add the chopped scallion and sauté until softened and translucent, about 3–4 minutes.

Stir in the minced garlic and red chili flakes, cooking for about 1 minute until fragrant.

Pour in the white wine and bring to a simmer. Let it cook for 2–3 minutes to reduce slightly and allow the alcohol to evaporate.

Stir in the hand-crushed San Marzano tomatoes with their juices. Bring the mixture to a gentle boil, then reduce heat and simmer for about 5 minutes to allow the flavors to blend.

Add the cleaned mussels to the pot. Cover and cook until the shells open, about 6–8 minutes. Discard any mussels that do not open.

Stir in the fresh basil or parsley and season with salt and pepper to taste.

Serve immediately with crusty bread for dipping. If desired, finish with a few delicate shavings of Parmesan for a light salty contrast.