Boil elbow noodles in salted water, stopping 2 minutes early. Drain and set aside—no rinsing or oil.
Combine beef, sausage, eggs, breadcrumbs, Parmesan, salt, and pepper. Mix gently.
Roll into 1″ balls (about 30). Broil on oiled sheet for 5–6 minutes, shaking halfway, until browned and 160°F.
Melt butter, whisk in flour for 1 minute. Slowly add milk; simmer until thickened.
Off heat, stir in shredded cheese. Season with salt, pepper, and nutmeg.
Mix pasta with sauce, add to dish, top with meatballs. Bake at 325°F for 20 minutes. Optional: broil to brown top.