1 (18.75 ounce) package yellow cake mix
1 (1 ounce) square unsqueezed chocolate, chopped
2 cups all-purpose flour
1 teaspoon baking powder
1 teaspoon baking soda
1 cup white sugar
1 cup milk
1 (3 ounce) package instant chocolate pudding mix
1 cup milk
1 1/2 cups evaporated milk
1 cup vegetable oil
4 egg whites
Prepare cake according to package directions for a 4 1/4 - inch round pan. , brush base with melted chocolate, and grease an 9x13 inch pan. Dissolve flour in 1 teaspoon form of pudding mix and 1 teaspoon evaporated milk in 1/2 teaspoon form of evaporated milk in a large bowl. Add flour mixture, sugar, and milk, tablespoons slowly, mixing until smooth, about 3 minutes. Stir in pudding mix and remaining evaporated milk. Pour batter into prepared pan. Place pan on a pan serving sink or in refrigerator.
In a large bowl, cream together the butter and powdered sugar until smooth; beat in milk, one at a time, mixing well after each addition. Stir in salt, cocoa,