Spiced Beef is a unique quest item found in The Elder Scrolls V: Skyrim. It can be found at Markarth Stables where Banning sells Vigilance, a war-dog. If the Dragonborn asks him how long he has trained dogs, he will remember he has a delivery to make to Voada in Understone Keep. If the Dragonborn accepts to help him, he will hand over the spiced beef.
The spiced 'beef' is actually human meat. This is discovered after completing "The Taste of Death," Namira's Daedric Quest. Banning is one of the cannibals in the Coven of Namira, and when he is asked about the beef, he replies with, "Ah yes. The courier. I guess you know my secret ingredient for that spiced beef, now."
Once the food has been given to Voada, she will give 500 as reward and suggest to buy the dog with it. The spiced beef can be pickpocketed from Voada afterwards.