Bring a large pot of salted water to boil. Your water should taste like sea water for properly seasoned pasta.
While waiting for water to boil, prep shrimp: Pat shrimp dry with paper towels, season with salt and pepper, and ensure shrimp are completely thawed if frozen.
Cook fettuccine according to package directions until al dente (usually 10-12 minutes). Reserve 1 cup of pasta water before draining.
While pasta cooks, prepare the shrimp: Melt 2 tablespoons butter in a large skillet over medium-high heat, add shrimp and cook 2-3 minutes per side until pink and slightly curled, remove shrimp and set aside.
Make the Alfredo sauce: In the same skillet, add remaining butter and minced garlic, sauté garlic until fragrant (about 30 seconds), pour in heavy cream and bring to a gentle simmer, gradually stir in both cheeses until melted and smooth.
Combine everything: Add cooked pasta to the sauce, toss until well coated, adding pasta water if needed to reach desired consistency, fold in the cooked shrimp, season with additional salt and pepper to taste.