From:
The Thorough Good Cook
Sauces 7. Béarnaise
Mix half a
teaspoonful of
flour with a little
butter. Moisten with
mushroom juice, and let it boil for a few minutes; thicken with the
yolks of one or two
eggs beaten up in
cream. Add a few
mushrooms,
truffles chopped up fine, some
essence of
anchovy, and the
juice of a lemon.