Trenette with smothered onion sauce

Marcella Hazan's recipe for a smothered onion pasta sauce is one of my all-time favorites.   Sliced onion is sweated with butter and olive oil for an hour or so on very low heat, and then "browned" on medium high heat until golden.  The sweating caramelizes the onion and makes it very soft and sweet, while the browning gives it a deeper flavor.

Other flavor comes from white wine (cooked into the golden onion until fully reduced), black pepper, grated parmesan, and parsley.