I found this recipe off of the Olive Garden website. I used it for Alyx's dinner too and it was also very yummy.
1 1/2 cups milk
1 1/2 cups heavy cream
1/2 cup fresh Parmesan cheese, grated
1/2 cup fresh Romano cheese, grated
6 egg yolks from jumbo eggs
Salt and black pepper to taste
Heat milk and cream in a heavy bottom saucepan until it begins to simmer. Turn off heat. Slowly whip in cheese, then remove from heat. Place egg yolks in a separate bowl and slowly whip in a portion of the hot milk and cream mixture. Slowly add egg yolk mixture back into remaining cream mixture. Place back on very low heat and continually stir until simmering. Take sauce off heat so it thickens. Season to taste with salt and black pepper. Serve over your favorite pasta.