Decadent Chocolate Cake
["1 c. boiling water", "3 oz. unsweetened chocolate", "8 Tbsp. butter", "1 tsp. vanilla extract", "2 c. sugar", "2 eggs, separated", "1 tsp. baking soda", "1/2 c. sour cream", "2 c. less 2 Tbsp. unbleached all-purpose flour, sifted", "1 tsp. baking powder"]
["Preheat oven to 350\u00b0.", "Grease and flour a 10-inch tube pan. Pour boiling water over chocolate and butter; let stand until melted.", "Stir in vanilla and sugar, then whisk in egg yolks, one at a time; blend well after each addition.", "Mix baking soda and sour cream; whisk into chocolate mixture.", "Sift flour and baking powder together and add to batter, mixing well.", "Beat egg whites until stiff.", "Stir 1/4 of the egg whites into batter.", "Scoop remaining whites on top of batter and fold in.", "Pour batter into prepared pan.", "Place on middle rack in oven and bake for 40 to 50 minutes.", "Cool in pan for 10 minutes; unmold and cool completely. Frost."]
["boiling water", "unsweetened chocolate", "butter", "vanilla extract", "sugar", "eggs", "baking soda", "sour cream", "flour", "baking powder"]