Potato Soup
["1/2 c. butter or margarine", "1/2 c. minced onion", "1 Tbsp. salt", "4 c. cubed raw potatoes", "1 1/2 c. water", "2 c. hot milk", "1 egg yolk, slightly beaten", "1/2 c. cold milk", "1/8 tsp. pepper", "2 Tbsp. chopped, fresh parsley"]
["Melt butter in a heavy saucepan over moderately low heat (225\u00b0).", "Add onions and cook until soft.", "Add salt, potatoes and water.", "Cover, cook over moderately low heat (225\u00b0), stirring occasionally, until potatoes are tender, about 30 minutes.", "Stir in hot milk.", "Combine egg yolk and cold milk.", "Gradually add to hot soup, stirring constantly.", "Garnish with parsley before serving.", "Serves 6 to 8."]
["butter", "onion", "salt", "potatoes", "water", "hot milk", "egg yolk", "cold milk", "pepper", "parsley"]