Germans Sweet Chocolate Cake
["1 (4 oz.) bar Baker's sweet chocolate", "1/2 c. boiling water", "1 c. butter", "4 egg yolks, unbeaten", "2 1/2 c. sifted Swans Down cake flour", "1/2 tsp. salt", "1 c. buttermilk", "2 c. sugar", "1 tsp. vanilla", "1 tsp. baking soda", "4 egg whites, stiffly beaten"]
["Melt chocolate in boiling water.", "Cool.", "Cream butter and sugar until fluffy.", "Add egg yolks one at a time, and beat well after each.", "Add melted chocolate and vanilla.", "Mix well.", "Sift together flour, salt and soda.", "Add alternately with buttermilk to chocolate mixture; beat well.", "Beat until smooth.", "Fold in whites.", "Pour into 3 deep 8 or 9-inch layer pans, lined on bottoms with paper.", "Bake in moderate oven on 350\u00b0 for 30 to 40 minutes.", "Cool.", "Frost tops only."]
["chocolate", "boiling water", "butter", "egg yolks", "flour", "salt", "buttermilk", "sugar", "vanilla", "baking soda", "egg whites"]