Bring A Large Pot Of Lightly Salted Water To A Boil. Add Fettucine Pasta And Cook For 8 To 10 Minutes Or Until Al Dente; Drain. In A Large Skillet Melt The Butter And Add The Chopped Garlic. Cook On Low For About 5 Minutes, Stirring Often, Making Sure Not To Burn The Garlic. Pour About A 1/4 Cup Of The Heavy Cream Into A Small Bowl. Add The Egg Yolk And Beat Together; Put Aside. Pour The Remaining Cream Into The Frying Pan. Increase The Heat To Medium-High. As The Cream Starts To Boil, Mix Rapidly Using A Whisk. Slowly Add The Cream/Egg Mixture. You Do Not Want The Egg To Curdle. Continue Whisking Until Well Blended. Add 1 Cup Of The Parmesan Cheese And Continue To Mix The Cream. Pour In The Remaining Parmesan And The Parsley, Mix Until Smooth. Immediately Remove From Stove. Serve Over Cooked Pasta.