Boil salted water in a pan. Add the fetuccini pasta and boil for a bout 8 to 10 minutes until the water is drained. In a large skillet chop the garlic and melt the butter. Cook that for about 5 minutes. Make sure you dont burn the garlic and stir it gently. Pour 1/4 of a cup of heavy cream into a large bowl. Add the egg yolk and beat it together. Put that aside and add the rest of the cream into the frying pan. Increase the heat and as the cream starts to boil, mix it rapidly with a whisk. Whisk it until it is all mixed good.
Add one cup of parmesan cheese and continue to mix the cream.Pur the rest of the parmesan and parsley until it is smooth. Immediately remove it from the stove and serve over cooked pasta :).