In a 6 to 8-quart, heavy-bottomed saucepan, heat the olive oil and butter over medium heat. Add the onions, celery, and garlic and sweat over medium heat until the vegetables are translucent and soft but not browned, about 10 to 15 minutes. Add the veal, pork, and pancetta and stir into the vegetables. Add the meat over high heat, stirring to keep the meat from sticking together until browned. Add the tomato paste, milk, and wine and simmer over medium-low heat for 1 to 1 1/2 hours. Season with salt and pepper, to taste, and remove from the heat.
When ready to use, the cooked pasta should be added to a saucepan with the appropriate amount of hot ragu Bolognese, and tosses so that the pasta is evenly coated by the ragu.