Begin by preparing the marinade for the beef. In a large bowl, combine soy sauce, vinegar, freshly minced garlic, sliced onion, tomato puree, olive oil, black pepper, salt, and bay leaves. Whisk these ingredients together until the mixture is well blended and aromatic. Cut your beef into even cubes to ensure uniform cooking. Add the beef cubes to the bowl with your marinade, making sure each piece is thoroughly coated. Cover and allow the beef to marinate for at least one hour, or longer if time permits, to let the flavors deeply infuse the meat. After marination, transfer the beef along with the marinade into a large pot. Add water to the pot to create a stew-like consistency. Bring the mixture to a boil over medium-high heat, then reduce the heat to low. Cover the pot and let it simmer gently for about 1 to 1.5 hours, or until the beef is tender. Halfway through cooking, peel and cut the potatoes into chunks and add them to the pot. They will cook in the flavorful sauce and absorb its rich taste. Stir occasionally to prevent sticking and to evenly distribute the flavors. Once the beef is fork-tender and the potatoes are cooked through, squeeze a slice of fresh lemon over the stew to enhance the tanginess and depth of flavor. Adjust seasonings if needed. Serve your sumptuous Beef Mechado hot, ideally over a bed of saffron rice or steamed white rice. Garnish with fresh herbs if desired, and enjoy this comforting Filipino classic with your loved ones. Tip: For an extra layer of flavor, consider browning the beef cubes briefly before marinating to develop a caramelized crust that enriches the stew's taste.