Melt butter in a saucepan, add flour, and cook for a few minutes to form a brown-blond (roux blond) sauce. Add boiling stock, salt, pepper, and cook, stirring with a whisk. Add mushrooms and cook slowly, occasionally stirring, skimming, until sauce is reduced by 2/3 and is very thick and creamy. Strain through a fine sieve.{$7e}(Original recipe for 4)
