Preheat oven to 375°. In a large bowl, crumble beef. Add eggs, onion, bread crumbs, Parmesan cheese, garlic and seasonings; mix lightly but thoroughly. Shape into 2-in. balls. Place meatballs on greased racks in shallow baking pans. Bake, uncovered, until browned, about 25-30 minutes.
Meanwhile, in a skillet or saucepan, melt butter over medium-low heat. Stir in cream, 1/2 cup Parmesan cheese, Romano cheese, nutmeg and 1/8 teaspoon pepper. Bring to a simmer; remove from heat.
In a small bowl, whisk egg yolks; slowly pour 1 cup of hot cream mixture into egg yolks, whisking constantly. Return all to the pan, whisking constantly. Cook and stir over medium-low heat until sauce has thickened slightly and a thermometer reads 160°.
Toss meatballs with alfredo sauce; sprinkle with remaining 1/4 cup Parmesan cheese. If desired, serve with hot cooked pasta and garnish with parsley.