Heat oil and butter in a large saucepan over med heat. Add bacon, garlic and sage; cook for 3-5 min until fragrant and fat has rendered. Stir occasionally to prevent garlic from burning. Add onion, carrot and celery and sauté for 3-4 min. Add beef and sausage and brown, breaking into small pieces with a spoon. Do not drain.
Stir in tomato paste, then add wine and cook until reduced by ¾. Add beef stock and season with salt and pepper. Simmer for 20-30 min, stirring occasionally until sauce has thickened, but is still moist. Sauce should be oily.*
Meanwhile, fill a large pot with water, salt well and bring to a rolling boil. Add Tagliatelle and cook according to package directions, approx. 7-8 min for al-dente pasta.
Drain pasta, return to pot and add sauce. Combine well and serve.
*Health conscious Americans are used to draining off fat as they cook meats, whereas in Italy, if the meat is good quality, the fat is often used to add deep flavor to the dish, lubricate the pasta, and create a hearty, comforting rustic meal. It is also said that this whets the palate before drinking a robust wine. It is recommended that the fat be retained in this recipe for these reasons, and that high quality meats are used for best results.