Melt butter in medium saucepan, blend in flour and cook, stirring over medium heat until bubbly; do not let mixture brown.
Meanwhile, bring milk to a boil in another saucepan.
Add hot milk to butter-flour mixture and cook, stirring over medium heat until sauce thickens and is smooth.
Lightly beat egg yolks and stir into sauce.
Then stir in cheese and cauliflower until smooth.
In a large bowl, beat egg whites until stiff but not dry.
Fold cauliflower mixture gently but thoroughly into beaten egg whites.