Most people only know about the Venkateshwara form of Vishnu (AKA Balaji or Srinivasa) in connection to the deity of the world-renowned Tirumala Venkateshwara Temple in Tirupati. But that is not the first time that Vishnu has come to earth in his Venkateshwara form; he came earlier as Upilliappan, the deity of the great Upilliappan Vishnu Temple near Kumbakonam in Tamil Nadu. The story as I understand it goes roughly as follows. Once the sage Markandeya prayed that he would have Lakshmi as a daughter and Vishnu as a son-in-law. Sure enough, Lakshmi took an incarnation as a baby born from the earth, whom Markandeya named Bhumadevi (not to be confused with Vishnu's wife Bhumidevi goddess of the earth). When Bhumadevi became a young girl, Vishnu went in his Venkateshwara form to Markandeya and asked for his daughter's hand in marriage. Markandeya said that his daughter was so young, and that she didn't even know how to put salt in her cooking. But Vishnu said that he was willing to eat without salt, for which he came to be known as Upilliappan or the lord without salt.
But my question isn't about the story itself, but rather what scripture the story is found in. I just visited the Upillaiappan Vishnu Temple, and this is what the Sthala Purana (temple scripture) of the temple says:
History of the holy place found in Brahmanda Purana
Narada's prayer to Brahma
Once Narada prayed to Brahma to enlighten him on the history and and greatness of the holy Markandeya kshetra that will also be for the benefit of humanity.
On hearing this, Brahma started narrating the greatness of Tiruvinnagar and its presiding deity, whose glory can not be described even by Adisesha with his 1000 tongues.
And then it proceeds to tell the story of Upillaiappan in far more detail than I gave above. My question is, where in the Brahmanda Purana does this story occur? Here are all five volumes of the Motilal Banarsidass translation of the Brahmanda Purana, most of the links being taken from DSpace, the digital repository of the West Bengal Public Library network: