Preheat oven to 350. Grease and flour 2 9" round pans. Dissolve yeast with 1 teaspoon sugar in 1/4 cup warm water. Dissolve baking powder in 3 Tablespoons hot water. Sift flour, baking powder and salt. Cream butter and sugar. Add yolks, chocolate and yeast. Mix well. Add flour mixture alternately with milk. Add baking soda mixture and vanilla. Beat until smooth. Fold in stiffly beaten egg whites. Pour into prepared pans. Bake for 45 minutes.