If we stick to a single game, VfL Bochum - Bayern München in 1976 (11 goals). Bochum were 3-0 up by the half-time whistle and 4-0 in 53th minute. In the next 20 minutes, Karl-Heinz Rummenigge and Gerd Muller took Bayern to an unbelievable 5-4 lead.
Kaczor put Bochum level on 5-5 in the 80th minute and that seemed to be it, but with a minute to go Uli Höness scored his second and Bayern's sixth for their most amazing win ever.
Over two legs, and I'm only including it because of how amazing it sounds, Bayer Uerdingen - Dynamo Dresden in 1986. A team of numerous East German stars built a 2-0 lead in the first leg at home and then ran away with a solid 3-1 lead at half time, seemingly clinching the tie in the return game at Krefeld. Dynamo were 5-1 ahead on aggregate, and the 1-3 scoreline stood until the 57 minute. The Icelander Gudmundsson won that dubious penalty kick, which Wolfgang Funkel converted. Six minutes later Gudmundsson himself made it 3-3. Then the unlucky forward Minge deflected a shot into his own net, and the Easterners found themselves utterly disoriented amidst roars from the partisan crowd. Bayer attacked in waves and the reserve Klinger brought the temperature to boiling point with the fifth goal 12 minutes from time.
5-5 on aggregate, but Dynamo were still ahead on the away-goals rule.
Schäfer was knocked down in the area and Wolfgang Funkel again scored from the spot, making it 6-3 only 23 minutes after the scoreboard had shown the humiliating 1-3. Before the final whistle, in the total confusion, Schäfer picked up the seventh goal, ending up on the shoulders of his mates and the fans who invaded the pitch.
Bayer Uerdingen - Dynamo Dresden (12 goals).
Source: The Top 20 Most Amazing Soccer Comebacks