Sour Cream Chocolate Cake
["2 (1 oz.) sq. unsweetened chocolate", "1/4 c. hot water", "1 c. thick sour cream", "1 tsp. vanilla", "1 tsp. baking soda", "3 stiff beaten egg whites", "3 beaten egg yolks", "1 1/2 c. sugar", "1 3/4 c. sifted cake flour", "1/2 tsp. salt"]
["Melt chocolate in water over double boiler until chocolate melts; cool.", "Sift flour, soda and salt; set aside.", "Beat egg yolks with sour cream, adding sugar gradually, and beat vigorously until thick.", "Add chocolate mixture and vanilla mixing well.", "Add flour, soda and salt to sour cream mixture.", "Beat until smooth. Fold in stiffly beaten egg whites.", "Bake in paper lined 13 x 9 1/2 x 2-inch pan at 350\u00b0 for 45 minutes.", "Frost with chocolate butter cream frosting."]
["unsweetened chocolate", "hot water", "sour cream", "vanilla", "baking soda", "egg whites", "egg yolks", "sugar", "cake flour", "salt"]