*Try to use the sharpest cheddar you can find; the flavor of a mild cheddar will get lost.
In a deep, fairly wide-bottomed saucepan, cook the onion in the butter till it's softened and is beginning to brown, about 5 minutes. Stir in the flour, then the broth, cauliflower, salt, mustard and sherry or wine. Let the soup simmer for 15 minutes, or
Puree the mixture using a hand blender, or in a blender or food processor. Return the soup to the pot, and stir in the evaporated milk or cream and the cheese. Bring the soup to a bare simmer, and cook very gently just till the cheese melts, stirring all