This restaurant chain has achieved 12 straight years of unstoppable growth without playing the discount game

As the rest of the fast-food industry has gone crazy for deals, Wingstop has stayed steady - resulting in explosive growth.

On Thursday, the company reported that same-store sales increased 7.9% in 2015, the company's 12th consecutive years of growth.

In recent months, fast-food chains such as McDonald's, Burger King, and Pizza Hut have debuted discount options in an effort to win the fast-food price wars. Wingstop, meanwhile has stuck with the basics.

"I would not suggest that we've seen a particular time or event where aggressive discounting has impacted our business," Morrison said in response to a question about recent deals in an earnings call on Thursday. "But I'd like to think of Wingstop as existing in a category of one and all by ourselves. We don't have, as we mentioned, a true direct competitor that we fight against."

The company has been uncompromising in its dedication to a simple formula that works.

"When we started 21 years ago, we sold wings, sides, and fries," CEO Charlie Morrison told Business Insider last year. "We've had the same three sides on the menu since the beginning. We've added boneless wings over the years, and we've added two new flavors. That's innovation for us."

Wingstop's steady simplicity has helped make the company a prime candidate to grow digital sales.

Online and mobile orders make up about 15% of all domestic sales, more than double last year's figure. As 60% of Wingstop orders are still via phone and nearly half of Wingstop customers are millennials, this number will likely only grow in coming years.

"The pizza players are in the 50%-plus space," Morrison says. "I don't see any reason why we can't aspire to be up in that kind of echelon with them."

Wingstop's commitment to simplicity extends to the most important aspect of its business: the food.

The chain has 11 wing flavors, with a new limited-time offering added to the menu twice a year. The last flavor was Spicy Korean Q, which accounted for more than 5% of wings sales; the current one is a smoky dry rub named Smoke 9, which rolled out last week. There are just three sides: fries, beans, and coleslaw.

Wingstop competes with chains like McDonald's and Burger King, but not directly - in part because it has a very different business model. The chain doesn't need to debut flashy new menu items or slash prices with intense deals.

The chicken chain has established its own category not by competing, but through simplification - and that's serving the company just fine.