Fettuccine with Cream Sauce and Mushrooms

• 1 pound fettuccine (egg noodles)
• ½ Spanish onion, finely chopped
• butter

Sauté finely chopped onion in 2 tablespoons butter until transparent; add sliced mushrooms and diced ham, and continue to cook until mushrooms are tender, stirring from time to time. Combine double cream, egg yolks, ¼