signature dish

I often hear people talk of a dish as being indicative of the quality of the restaurant. Jeff Smith used Tom Ka Gai (chicken coconut soup) as the authenticity and quality indicator of a Thai restuarant for example.

Do you have a dish that you sample in a mexican restaurant to test quality and authenticity?

And if so, what would it be and what characteristics do you look for.

And if not, how would you counsel someone to judge a mexican restaurant?

I mean, I enjoy the americanized food but it's not authentic. How do I learn and judge authenticity and qualtiy when I don't have the opportunity to travel to Mexico? I don't trust my local restaurant critcs on the topic as authorities for Mexican food either.

My favorite Tacqeria, now out of business, served baked potatoes as a side dish. They seemed authentic, they had beef head meat, brains, tongue and the other fun meats for fillings, but the potato threw me.

Tasted good though.

Phil