1. In a small skillet, toast the peppercorns over moderately high heat until fragrant, about 30 seconds. Transfer to a spice grinder and let cool completely. Grind to a powder and transfer to a small bowl. Stir in the wine, black beangarlic sauce and sugar.
2. Light a grill. Arrange the steaks on a baking sheet and rub them all over with the sauce. Let stand for 10 minutes.
3. Season the flank steaks lightly with salt. Grill over moderately high heat, turning once, until the steaks are medium-rare, about 8 minutes. Transfer the steaks to a work surface and let rest for 5 minutes. Thinly slice the meat across the grain and serve.