Heat the olive oil in a large pot over medium heat.
Add the sliced onions and cook until they become golden and caramelized, about 20 minutes.
Add the beef chunks to the pot and brown them on all sides.
Stir in the tomato paste and cook for another 2 minutes.
Pour in the beef broth and add salt and pepper. Bring it to a simmer.
Reduce the heat to low and let it cook slowly for about 1.5 hours, stirring occasionally.
Cook the pasta in a separate pot until al dente according to package instructions. Drain well.
Combine the pasta with the beef and onion sauce, mixing well to coat the pasta evenly.
Serve hot, garnished with fresh parsley or grated cheese if desired.