Earlier this week, papers filed with the SEC showed that a group of investors have purchased a 9.5% stake in Steak n Shake (NYSE: SNS). Steak n Shake is a major American restaurant chain, with nearly 500 locations throughout the Midwest and southern US.

The SEC documents indicate that HBK Management LLC leads a group of investors who have paid $412 million for 2.7 million shares of the company. HBK, based in Dallas, Texas, manages roughly $13 billion in equity capital, making it one of the larger private investment funds. The firm is named after Harlan B. Korenvaes, former Managing Director of Merrill Lynch & Co. (NYSE: MER). He founded HBK in 1991, starting with $30 million in capital.

Steak n Shake shares surged on news of the investment. Share prices had fallen in May with the company's announcement of reduced guidance for 2007 earnings, and were trading in the $15 range before the new investment. Shares have rebounded to the $17 level, up roughly 15%.

Steak n Shake is headquartered in Indianapolis. It offers a hybrid of fast food and restaurant dining, with made-to-order hamburgers (the justly famous "Steakburger"), real silverware, and milkshakes that actually contain milk. The investors say they have no plans to take control of the company, but rather seek to develop new strategies to improve the company's performance.