Mushroom Sauce - cooking recipe

Ingredients

1 pt. white sauce
4 oz. mushrooms
1/2 butter or margarine
salt
a little lemon juice
1 egg yolk
2 Tbsp. cold water or cream

Preparation

Prepare and slice mushrooms.
Saute them in fat until done. Then add them to the white sauce.
Season with salt and lemon juice.
Add egg yolk, beaten with water or stir in cream.