Quarter one onion; stuff the cloves into the second onion. In a large saucepan, combine water and broth; add onions, leeks, carrots, and seasonings. Bring to a boil. Reduce heat; cover and simmer for 15 minutes. Add cauliflower; simmer uncovered for 30 minutes or until vegetables are tender. Remove from heat.
In a small bowl, combine cornstarch and cream until smooth. Stir in egg yolks. Stir in a small amount of hot soup into cream mixture, return all to the pan, stirring constantly. Simmer uncovered for 15 minutes. Discard the whole onion.
Ladle soup into individual ramekins. Top with cheese strips. Broil 4-6 inches from the heat for 3-5 minutes or until cheese is bubbly. Serve immediately.