1. Prepare grill for cooking. If using a charcoal grill, open vents on bottom of grill.
2. Mash together bread crumbs, vinegar, capers, garlic, anchovy paste, and mustard using a mortar and pestle (or see cooks' note, below). Add parsley, oil, and salt and pepper to taste and stir until combined well. Stir in water.
3. Pat steak dry and season on both sides with salt and pepper. When fire is hot (you can hold your hand 5 inches above rack for 1 to 2 seconds), grill steak on lightly oiled grill rack, uncovered, turning once, about 10 minutes total for medium-rare. Let stand 10 minutes.
4. Stir sauce and serve with steak.

Yield: 1 servings