How to Make It
In a medium saucepan, combine the vinegar, dry mustard and cloves and simmer over moderate heat until reduced by half, about 10 minutes. Transfer the vinegar to a heatproof bowl. Wipe out the saucepan.
Add the 2 tablespoons of oil to the saucepan, along with the onion, garlic and cumin. Cook over moderately low heat until the onion is softened and fragrant, about 5 minutes. Add the brown sugar and tomatoes and cook until softened, about 5 minutes. Add the reduced vinegar and the barbecue sauce and simmer until reduced to 2 cups, about 5 minutes. Transfer the sauce to a blender and puree until smooth. Add the sambal oelek and season with salt and pepper.
Light a grill or preheat a grill pan. Rub the steaks with oil and season generously with salt and pepper. Grill over moderately high heat, turning once, until the steaks are lightly charred and medium-rare, about 6 minutes total. Let the steaks rest for 5 minutes, then garnish with rosemary and serve with the barbecue sauce.