Preheat oven to 350 °. In a large bowl, combine eggs, milk, bread crumbs and seasonings; set aside. In a skillet, saute onion in butter until soft; add to egg mixture. Add beef and ground pork; mix well. Cover and refrigerate 1 hour.
Preheat oven to 350°. Shape meat mixture into 1-1/4-in. to 1-1/2-in. balls. Place meatballs on a greased rack in a shallow baking pan. Bake, uncovered, 20-25 minutes or until a thermometer reads 160°. Remove from oven and place in a 3-qt. baking dish.
For sauce, melt butter in a saucepan; stir in flour to form a smooth paste. Gradually stir in broth; bring to a boil, stirring constantly. Reduce heat; stir in cream, dill, salt and pepper. If a thicker sauce is desired, continue cooking 10-15 minutes, stirring occasionally. Pour sauce over meatballs.
Bake, uncovered, 40-45 minutes or until heated through and bubbly. Garnish with fresh dill if desired.