Bring a large pot of salted water to a boil. Add the fettuccine and cook according to the package instructions until al dente. Reserve about a cup of pasta water before draining the pasta in a colander.
In a large skillet over medium heat, melt the unsalted butter. Once melted, add the minced garlic and sauté for about 1-2 minutes until fragrant, being careful not to burn it.
Reduce the heat to low and pour in the heavy whipping cream and milk. Stir well to combine. In a small bowl, mix the cornstarch with a few tablespoons of the pasta water until dissolved, then add it to the skillet. This will help thicken the sauce.
Stir in the cream cheese (if using) until melted and smooth. Then, add the dried basil, dried parsley, onion powder, dried oregano, salt, pepper, red pepper flakes, and ground nutmeg. Mix until everything is well incorporated and the sauce is heated through.
Gradually add the freshly grated Parmesan cheese, stirring constantly until melted and the sauce is creamy. If the sauce is too thick, add a little reserved pasta water to reach your desired consistency.
Add the cooked fettuccine to the sauce in the skillet. Toss gently to coat the pasta evenly with the sauce. Let it cook together for another minute or two, allowing the flavors to meld.
