Good-Cooking - Banana Whoopie Pies

Ingredients

• 4 1/2 cups all-purpose flour
• 1 teaspoon salt
• 2 teaspoons baking powder
• 1 teaspoon baking soda
• 1 cup shortening
• 2 cups granulated sugar
• 2 large eggs
• 2 cups mashed extra ripe bananas
• 1/2 cup sour milk or buttermilk
• 1 teaspoon vanilla extractFilling
• 2 egg whites
• 1 (1 pound) box confectioners' sugar
• 4 tablespoons milk
• 1 teaspoon vanilla extract