Cook the fettuccine or spaghetti according to package instructions until al dente. Drain and set aside, reserving 1/2 cup of pasta water.
In a large skillet, heat the olive oil over medium heat. Add the minced garlic and sauté for about 1 minute until fragrant, being careful not to burn it.
Pour in the heavy cream and bring to a gentle simmer. Stir in the grated Parmesan cheese, salt, black pepper, and red pepper flakes (if using). Mix well until the cheese is melted and the sauce is smooth.
Add the cooked pasta to the skillet, tossing to coat the pasta evenly with the sauce. If the sauce is too thick, gradually add some reserved pasta water until you reach your desired consistency.
Remove from heat and garnish with chopped parsley before serving.