Sauté the onion in half the butter and oil, add garlic and simmer for 30 seconds. Mix in the tomato paste, thyme, and stock. Cut steak into very small pieces. Sauté in the remaining butter and oil until browned on the outside and still pink inside. Cook the spaghetti in boiling water for five minutes and drain in colander. It will not be completely cooked through. Mix the spaghetti, meat mixture, and sauce together in a large foil baking pan. Add the Parmesan cheese and additional butter. Seal tightly with heavy-duty foil and bake at 350° for 15 to 20 minutes until the pasta is cooked.