Cook lasagna noodles; drain and return to pan. Cover with cold water. Combine ground chuck, 2/3 cup flour, salt, thyme, and eggs in large bowl. Beat at medium speed with electric mixer until blended. Gradually beat in milk and onion. Drain noodles.
Lightly oil a 6-cup ring mold. Line mold with noodles by placing them crosswise so each noodle extends over outer edge on bottom of mold. Fill center with meat mixture. Bring noodles over filling to enclose mixture. Cover with foil. Bake at 350 degrees for 1 hour.
Melt butter; stir in 3 tablespoons flour. Cook until bubbly, stirring constantly. Gradually stir in milk and broth. Cook until bubbly. Spoon over lasagna. Serves 8.
