In a small saucepan, combine the wine, vinegar and demiglace and bring to a boil. Simmer over moderate heat until the sauce is reduced to a thick glaze (about 1/2 cup), about 20 minutes. Season the glaze lightly with salt and pepper.
In a heavy skillet, melt the butter. Lightly season the steaks with salt and pepper and add them to the pan. Add the garlic and cook over moderate heat, turning the steaks occasionally, until browned and crusty all over and an instant-read thermometer inserted in the center registers 130° for medium-rare, about 14 minutes. Transfer the steaks to a platter and let rest for 5 minutes; discard the garlic. Transfer the steaks to plates and serve with the fig-balsamic sauce.
2 cups dry red wine
2 tablespoons fig balsamic or plain balsamic vinegar
2 tablespoons beef or veal demiglace, (see Note)
Freshly ground pepper
4 tablespoons unsalted butter
4 (5 ounces each) bison tenderloin steaks
4 (large) garlic cloves, lightly smashed