Heat the olive oil and butter in a large pan over medium heat. Add the finely minced shallots and garlic, sautéing for about 1 minute until fragrant and translucent.
Stir in the thinly sliced fennel and a teaspoon of sea salt. Cook for 2 minutes until softened. Add the sliced red pepper and chili flakes, sautéing for another 3 minutes.
Pour in the white wine and let it simmer for 1–2 minutes to allow the alcohol to evaporate, leaving behind a rich, acidic base.
Stir in the double cream, remaining sea salt, garlic powder, and dried oregano. Bring to a gentle simmer for 1 minute until the sauce begins to thicken slightly.
Fold the fresh tagliatelle into the sauce. Toss gently for 2 minutes, ensuring the noodles are well-coated and starting to absorb the flavors.
Add the frozen mussel meat and fresh parsley. Cover the pan with a tight-fitting lid and turn the heat to low. Let it sit for 3 minutes to perfectly steam and thaw the mussels.
Give the pasta a final toss and serve immediately in warm bowls with lemon wedges on the side for an extra burst of freshness.
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Notes
Frozen vs. Fresh: This recipe is specifically optimized for pre-cooked, shelled frozen mussel meat. If you use fresh mussels in the shell, you must steam them first until they open, then discard the shells before adding the meat to the pasta in Step 6.
The "Lid" Trick: Don't skip covering the pan with a lid at the end. The steam is what thaws the frozen mussels gently without making them rubbery. If the sauce looks too thick after steaming, add a tablespoon of pasta water or a splash of milk to loosen it.
Dry Pasta Substitute: If you are using dried tagliatelle instead of fresh, boil it in a separate pot of salted water until al dente (usually 2 minutes less than the package instructions). Drain it and add it to the sauce at Step 5.
Fennel Substitution: If you don't like the taste of fennel, you can use finely sliced leeks or celery for a similar aromatic crunch.
Wine Selection: Use a dry white wine like Pinot Grigio or Sauvignon Blanc. For a non-alcoholic version, replace the wine with an equal amount of chicken or vegetable stock and the juice of half a lemon.
Storage: Store leftovers in an airtight container in the fridge for up to 2 days. Reheat gently on the stovetop over low heat with a splash of cream to keep the sauce silky.