In a separate pot, make a simple soffritto of onion (and if you like, some finely minced prosciutto or pancetta) in olive oil and butter until soft and translucent. (memoriediangelina.com)
I make two versions of Bolognese: Both take a while to make and both contain soffritto, a mixture of onions, carrots and celery. (tastingtable.com)
They add texture, take well to pickling, and can be sautéed in your everyday soffritto. (bonappetit.com)