Begin by making the fettuccini: Bring a large pot of water with six quarts of water to a boil. When it reaches a boil, add nine teaspoons of kosher salt and the fettuccini. Cook the fettuccini until it's just al dente. The time for this should be on the pasta box.
While the pasta cooks, make the Alfredo sauce: In a large skillet melt the butter. Add the onion and garlic and cook on low heat until the onion softens, about ten minutes. Add the cream and milk and cook on medium heat, until the mixture thickens about ten minutes.
As the sauce thicken, make the shrimp: In a bowl, mix together the shrimp, softened butter, and herbs and spices. Heat a cast iron pan on medium heat and cook the shrimp on both sides until they're pink and cooked through.
Into the Alfredo sauce, stir in the peas, Parmesan, fettuccini and the shrimp. Serve topped with extra Parmesan and the basil leaves.