How to make
Fry the flour in a little oil and dilute with hot broth. Add liquid and stir with a wire until you get desired consistency. Separately saute the mushrooms in a little oil. Add melted cheese and stir until the cheese is melted.
Add this mixture to the sauce and add the beaten yolks with the lemon juice. Stir constantly for 2 minutes and remove from the heat. Add salt, pepper and nutmeg to taste and, if desired, mix with 1 tablespoon butter.