In medium bowl, cream the butter til fluffy. Beat constantly while adding egg yolks, heavy cream and Parmesan, 1 Tbsp. at a time. Season with salt and pepper and blend thoroughly. Put cooked spaghetti in large heated serving bowl. Add the cheese mixture and toss thoroughly. For a cheesier taste, add more (1/2 cup) Parmesan cheese as you blend the spaghetti with the Alfredo sauce.
Note: Alfredo di Lelio is credited with originating the Alfredo sauce in 1914. A Rome restaurateur, de Lelio created this dish for his wife who lost her appetite during pregnancy. A rather extravagant character, di Lelio served his paper thin fettuccine with golden forks given to him by Mary Pickford and Douglas Fairbanks. His restaurant, still in operation, is run by his grandson who still serves this dish with golden forks. This recipe comes from the Secret Ingredient Cookbook.