Christmas dinner in an Austin restaurant
This list of restaurants that are open Christmas Eve and/or Christmas Day might be useful.
While I haven't been and can't personally vouch for it, the Green Pastures brunch might be nice (though I believe it is served buffet style). It's old-school Austin, located just south of downtown in a vintage house on a pretty piece of land, complete with peacocks. I'd imagine the menu would be similar to their Sunday Brunch:
Threadgill's is definitely a classic Austin experience as well.
Well for having never been to Austin before you can't go too wrong by stopping by Threadgill's on Christmas Day. The menu offers regional cooking (they have Chicken Fried Steak and Southern Fried Oysters on their Xmas list), and while it isn't "adventurous," it isn't a buffet either. Check out their special Christmas Holiday Menu at www.threadgills.com There is a North location at 6416 N. Lamar Blvd. which is about a 15 minute drive from the Arboretum area. They should be open 11 am.-10 p.m.