Cook the fettuccine according to packet directions until almost cooked through. Reserve 1 cup of the cooking water, drain, and set aside.
While the fettuccine is cooking, melt the butter in a large skillet over a medium-high heat. Add the chopped garlic and cook, stirring, for 1 minute or until fragrant. Add the flour and cook, stirring, until well combined.
Add the heavy cream, milk, parmesan cheese and Italian seasoning to the skillet. Simmer over a low heat for 5 minutes, or until slightly thickened.
Add the cooked fettuccine and 1/2 cup of the pasta cooking water to the cream sauce. Toss the pasta through the sauce for 2 minutes, or until the sauce is thick and silky, adding extra pasta cooking water if necessary.
Remove the skillet from the heat and serve the fettuccine immediately, garnishing with the fresh parsley, if using.