Mix liver spread with water in a bowl until a paste is formed. Add vinegar, brown sugar, soy sauce, bay leaves, salt, and pepper.

Heat olive oil in a saucepan over medium-high heat. Add onion and garlic; saute until onion is translucent, about 5 minutes. Add the vinegar mixture and let boil for 2 minutes. Stir until combined. Add bread crumbs. Reduce heat and simmer, uncovered, until sauce is thickened, about 20 minutes. Add cornstarch if necessary to thicken the sauce.