Cover and cook onions in butter in 4 Qt Dutch oven over medium-low heat 10 minutes. Stir in parsley, garlic, bay leaves and prosciutto. Cook, uncovered, over high heat 5 minutes, stirring frequently. Stir in remaining ingredients except cheese. Heat to boiling. Reduce heat. Cover and simmer 30 minutes, stirring occasionally. Remove bay leaves. Top each serving with cheese. Slow-simmering soup is enriched with diced prosciutto and freshly grated Romano cheese.