1. Mash bread and milk in large bowl with fork until homogeneous (you should have about 1/4 cup). Stir in salt, pepper, garlic, and steak sauce.
2. Break up beef into small pieces over bread mixture. Using fork or hands, lightly mix together until mixture forms cohesive mass. Divide meat into 4 equal portions. Gently toss 1 portion of meat back and forth between hands to form loose ball. Gently flatten into 3/4-inch-thick patty that measures about 4 1/2 inches in diameter. Press center of patty down with fingertips until it is about 1/2 inch thick, creating slight depression in patty. Repeat with remaining portions of meat.
3. Heat oil in 12-inch nonstick skillet over medium heat until just beginning to smoke. Add meat patties, indentation side up, and cook until well-browned, about 5 minutes. Using wide spatula, flip burgers and continue cooking, about 4 minutes for medium-well or 5 minutes for well-done. Distribute equal portion of cheese (if using) on burgers about 2 minutes before they reach desired doneness, covering skillet with lid to melt cheese. While burgers cook, toast buns. Serve on buns with desired toppings.