Suggest talking to the managers at
a) Komala Vilas or Annadaata for authentic, home-style Tamil (veggie) food.
b) the chettinad place in Milpitas if you want something spicier, more restaurant- than home-style.
c) Madura in Sunnyvale is another option
I'd avoid Saravanaa Bhavan (the business has a similar history as Pasand; why pamper them with your dollars)...
1020 E El Camino Real, Sunnyvale, CA 94087
I've attended Dosa parties catered by Udupi which were pretty good (better than rest.). Also, it's been a few a years, but a friend catered more traditional food from Panchavati in Sunnyvale which was very good (again, much better than rest.).
Lastly, have come across Annadaata's, but never tried them.
Are you looking for a full catering service, a cook to come to your house, or what?
I'd give the guys at Mayuri (Santa Clara) a call. They have a lot of flexibility and do banquets, specialize in south indian, and most of the locals are Tamil.
2230 El Camino Real, Santa Clara, CA 95050