Cream of Cauliflower Soup

• 1 cauliflower (about 2 pounds)
• 4 tablespoons butter

Poach cauliflower in boiling salted water for 5 minutes and drain. Melt butter in a saucepan; add flour and cook, stirring continuously, until a smooth paste is formed. Add chicken stock, coarsely-chopped onion, celery and parsley, and simmer for 20 minutes. Strain stock; add cauliflower and cook until cauliflower is softened. Rub soup through a sieve. Bring back to the boil; stir in 2 egg yolk