Today, Joe T. Garcia's has grown into a sprawling attraction with multiple rooms that can serve over 1,000 people a night. According to Lancarte, this is because his grandparents understood how to run a family business right from the beginning, and they passed that know-how down to the next generation.  "We've always believed in hands on, we like to stay hands on and control and watch everything that goes on in our kitchen," he said. He also noted that the restaurant's steady growth is the direct result of slow expansion.  "We're afraid if you grow too fast, too quick, then you can't handle what comes into the room," he said. "That's not a good thing."  Read More One-dish restaurants: Just a fad?  He added that the restaurant's simplicity has been an important factor in its growth.  "Back in 1935 when my grandparents started, I think we served a bowl of chili—one bowl—and just stayed one dinner," he said, "There's still just a small menu, actually no menu, which you know. It simplifies it. It makes it easier on our kitchens and we're able to get the food out there for the masses."  Read More Will farm-to-table work in Texas?  Tim Love agreed that the slow and steady approach of the restaurant's generations of owners was the key to its success.  "What I find unique about Joe T's is you guys started as a 'we serve dinner' shop," he said. "You see restaurants grow from one concept, and then they want to go out and do 30 of them around the country. It feels like Joe T. Garcia's took a different path…. It's an institution here, and if you want to eat Mexican food, or have some of the best margaritas, you come here."  Read MoreSigns that you're in a bad restaurant  —By Liza Hughes, special to CNBC
Every family has its secrets and the margarita recipe at Joe T. Garcia's has been guarded for almost 80 years, and even Tim Love will never find out what it is.