Prep the shrimp: Pat the shrimp dry with paper towels. Season with salt, pepper, and a pinch of red pepper flakes.
Dry shrimp sear better and stay juicy.
Boil the pasta: Bring a large pot of well-salted water to a boil. Cook fettuccine until just shy of al dente. Reserve at least 1 cup of pasta water, then drain.
Sear the shrimp: In a large skillet, heat olive oil over medium-high.
Add shrimp in a single layer. Cook 1–2 minutes per side until just opaque. Transfer to a plate.
Do not overcook.
Sauté aromatics: Reduce heat to medium. Add 1 tablespoon butter. Stir in shallot and cook until soft, about 2–3 minutes.
Add garlic and cook 30 seconds until fragrant.
Build the sauce base: Add tomato paste and cook, stirring, for 1 minute to caramelize. Pour in crushed tomatoes and a small splash of pasta water. Simmer 3–4 minutes to thicken slightly.
Add cream and season: Lower heat and stir in heavy cream and remaining red pepper flakes.
Season with salt and pepper. Simmer gently for 2–3 minutes until the sauce is silky.
Emulsify: Stir in the remaining 1 tablespoon butter and Parmesan until melted. Add more pasta water, a tablespoon at a time, to reach a glossy, loose coating consistency.
Combine pasta and shrimp: Add the drained fettuccine and shrimp to the pan.
Toss over low heat for 1–2 minutes. Add lemon juice and adjust seasoning to taste.
Garnish and serve: Sprinkle with chopped basil or parsley and extra Parmesan. Serve hot with lemon wedges.