Finely dice your onions and fennel.
Clean all shellfish throroughly.
Lightly sauté the onions, fennel, garlic and chiles. Be careful to not get color on the vegetables.
Add white wine and reduce by 50 percent.
Once wine has reduced, add tomatoes and cook until they start to break apart.
Add broth and allow bring to simmer very lightly, incorporating all the flavors together, about 45 minutes.
Taste and adjust salt and pepper to desired level.
Cook the linguini.
Transfer broth to a large, shallow pot and bring to a gentle simmer. Add the clams and cover, steaming for about 10 minutes until they're almost fully opened. Add the mussels and shrimp next. Bring to high simmer and cook for about 6 more minutes.
Add linguini to the pot and mix thoroughly with the broth and seafood. Add butter and grated parmesan cheese to thicken the sauce to your desired consistency. Check and adjust the salt and pepper to taste. Buon appetito!