Add pasta to a pot of salted boiling water and cook according to package instructions. Before draining, reserve 1/2 cup of the pasta water. Drain and set aside.
12 ounces fettuccine pasta
While the pasta is cooking, place the shrimp in a bowl with the seafood seasoning and toss to coat.
1 pound large shrimp, 1 tablespoon seafood seasoning
Place a large nonstick pan over medium high heat and add the oil. Once the oil is hot, add the shrimp in a single layer and cook, stirring, until the shrimp is cooked through, 2-3 minutes. Transfer to a plate and set aside.
1 tablespoon extra virgin olive oil
Turn the heat to medium-low and add the butter. Once melted, add the onions. Cook until soft and starting to brown, 3-5 minutes. Add the garlic and cook for an additional minute.
Add the white wine, scraping up any brown bits on the bottom of the pan, and cook until reduced to around 2 tablespoons of liquid. Add the flour and stir for 30-60 seconds. Stir in the cream, bring to a boil over medium heat while whisking, then whisk until the sauce thickens, 2-3 minutes. Turn off the heat and stir in the parmesan cheese until melted. Season with salt and pepper.
1/2 cup dry white wine, 1 tablespoon all-purpose flour, 2 1/4 cups heavy cream, 1/2 cup shredded or grated parmesan cheese, 1/2 teaspoon fine sea salt, 1/4 teaspoon ground black pepper
Add the pasta and shrimp to the pan, tossing to coat. If needed, stir in some of the pasta water to thin the sauce. Serve, topping with chopped parsley.