Preheat a large skillet over medium heat and add a bit of butter. Set aside.
In a bowl, combine breadcrumbs and milk. Let sit for a few minutes.
Add ground beef, onion, egg, salt, pepper, and nutmeg. Mix gently until combined.
Shape into small meatballs.
Cook meatballs in batches until browned and fully cooked. Remove and set aside.
In the same skillet, melt butter and whisk in flour. Cook until lightly golden.
Gradually add beef broth while whisking.
Stir in heavy cream and cook until smooth.
Return meatballs to the skillet and simmer until heated through.
Serve warm.