Quarter one onion; stuff the cloves into he 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 the heat.
In a 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 in. from the heat for 3-5 minutes or until cheese is bubbly. Serve immediately.