Alfredo Sauce - cooking recipe

Ingredients

1/2 c. Parmesan cheese
2/3 c. sour cream
1/4 lb. butter
1 egg yolk

Preparation

Beat egg yolk lightly; add yolk to sour cream.
Melt butter on top of stove in a saucepan.
Add sour cream mixture to melted butter.
Add Parmesan cheese and heat thoroughly.
Do not burn. Pour mixture over cooked pasta.