Heat your grill to medium-high. Brush each steak lightly with olive oil. Season the steaks with salt and pepper.
While the grill heats, make the glaze by placing the wine, shallot, garlic, pepper and rosemary in a small pot. Bring to a simmer and simmer until the wine has reduced by half. Stir in the cornstarch/stock mixture, return to a simmer, and simmer 1 to 2 minutes, or until lightly thickened. Reduce heat to low and cover the pot.
Grill the steaks to the desired doneness, allowing 2 to 3 minutes per side for rare, and 3 to 4 minutes per side for medium rare to medium. Plate the steaks and spoon the wine mixture overtop. Serve garnished with rosemary sprigs.