Key ingredients for classic Sauce Bolognese (Ragù Bolognese)?
Italy is very protective of its food heritage and there are many examples of recipes being officially codified by various authorities, e.g, the EU designation, Traditional Speciality Guaranteed, was applied to pizza margherita in 2009 and strictly mandates the ingredients that may be used. 

The recipe for Ragu alla Bolognese doesn't have the weight of the EU behind it but in 1982 the Bolognese chapter of the Accademia Italiana della Cucina did produce an official version and it is on their website, unfortunately only in Italian. Using Google translate you can see that the required ingredients are:

Lean minced beef, pancetta, carrot, onion, pureed or peeled tomato, dry white wine, whole milk, beef broth, olive oil or butter, salt, pepper, cream

I'll leave the translation of the instructions as an exercise for the reader lest I be accused of posting a recipe. ;-)