In a large stock pot melt butter and saute onions until tender. Add water and chicken granules, and bring to a boil. Measure out flour into a separate bowl and add some broth from stock pot to whisk together with flour. Slowly add flour mixture back into soup and add broccoli, cauliflower and carrots. Simmer until vegetables are tender. Add half and half cream, cheese and season with pepper. Heat through until cheese has melted being sure not to bring to a boil. Top with garlic croutons and serve.