Classic Cake-Like Brownies
["2 sq. (1 oz. each) unsweetened chocolate", "2/3 c. sifted all-purpose flour", "1/2 tsp. baking powder", "1/4 tsp. salt", "1/4 c. (1/2 stick) butter, softened", "1 c. sugar", "2 eggs, separated (at room temperature)", "1/4 c. milk", "1 tsp. vanilla", "1/2 c. broken walnut pieces"]
["Preheat oven to 350\u00b0.", "Melt chocolate in top of double boiler over simmering water.", "Remove and cool to room temperature."]
["chocolate", "flour", "baking powder", "salt", "butter", "sugar", "eggs", "milk", "vanilla", "broken walnut pieces"]