To prepare the fettuccine, bring a large pot of water to a rolling boil over medium-high heat. Add the pasta along with 1 teaspoon salt, and cook according to the package instructions until al dente, which should take about 3 minutes for fresh fettuccine. Drain the pasta in a colander, and do not rinse.

For the creamy shrimp Alfredo sauce, heat olive oil in a large cast-iron skillet over medium-high heat. Cook the shrimp in the hot oil, stirring frequently until they turn orange, which should take about 2-3 minutes. Add the minced garlic, chopped onions, and parsley, stirring until the onions are soft and translucent, around 2-3 minutes.

Next, incorporate the melted butter, cream cheese, and heavy whipping cream into the skillet. Stir the mixture well and cook for about 2 minutes until it reaches a smooth consistency. Mix in the Parmesan cheese and ground black pepper, stirring for an additional minute as the sauce begins to thicken. (Alternatively, you can use store-bought Alfredo sauce instead of making it from scratch.)

Turn off the heat and leave the sauce mixture in the skillet. Add the cooked fettuccine to the sauce, tossing to combine thoroughly. Season with salt flakes to taste. If you prefer not to bake, you can serve the pasta immediately at this stage.

For a pasta bake, sprinkle the chopped fresh mozzarella evenly over the fettuccine. Place the skillet under the broiler and cook on high for 2-3 minutes, watching closely until the cheese is melted and golden brown.