Melt butter in saucepan over medium heat. Blend in flour to make a roux. Add half-and-half all at once, stirring constantly until thickened and smooth. Add Parmesan, sherry, Worcestershire sauce, garlic powder and salt and pepper. Temper egg yolks with 2 tablespoons of hot mixture and add back to the cheese sauce. Set aside. Mix artichoke hearts, shrimp, and mushrooms together.