In a large deep skillet or Dutch oven, combine the fettuccine pasta, whole milk, chicken broth, minced garlic, salt, black pepper, and crushed red pepper flakes.
Bring the mixture to a boil over medium-high heat, stirring occasionally to prevent the pasta from sticking.
Reduce the heat to medium-low and simmer uncovered, stirring frequently, until the pasta is tender and most of the liquid has been absorbed, about 15 to 18 minutes.
Remove the skillet from heat and stir in the unsalted butter and grated Parmesan cheese until melted and the sauce is creamy.
Taste and adjust seasoning with additional salt and pepper if needed.
Sprinkle chopped fresh parsley over the top before serving.