Boil fettuccine noodles al dente according to directions on package. Drain pasta.
In a large frying pan, heat up olive oil over medium heat. Add minced garlic, and sauté one minute or until fragrant. Add flour and stir for an additional minute.
Whisk in chicken broth and milk, stirring until combined. Allow the mixture to simmer. Continue stirring until thickened.
Remove mixture from heat and pour into a blender. Add in nutritional yeast (I recommend starting with 1 1/2-2 tablespoons, adding more if you prefer), salt and pepper. Mix ingredients in the blender until combined well.
Pour sauce into the pan with the pasta. Toss to evenly coat the pasta. Serve topped with parsley, if desired.
Notes
You can mix in chicken or bacon if you want to add more texture or flavor to your pasta.