Cafe do Brasil seems to have shut down :( so I have changed it now to the beautifully set Fischerhütte located right beside Schlachtensee, in Zehlendorf.
Before you RSVP, please look at the location!
And take note of the price - it is 24,90€ for an all-you-can-eat, which includes a glass of sekt, and unlimited tea and coffee.
However, there will be items on the menu you can order if you don't want to go for the buffet.
Nearest stops: U-Bhf. Krumme Lanke, S-Bhf. Mexikoplatz, or you can take the buses 112, 629.