Banana Whoopie Pies

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 extract

Filling:
2 egg whites
1 (1 pound) box confectioners' sugar
1 cup shortening
4 tablespoons milk
1 teaspoon vanilla extract

Heat oven to 350 degrees F. Lightly grease and flour a cookie sheet.

In a large bowl sift together flour, salt, baking powder and baking soda; set aside.

In a large mixing bowl combine and cream together shortening and sugar. Add and beat thoroughly eggs, bananas, sour milk and vanilla extract. Add dry ingredients gradually, beating after each addition.

Drop by heaping teaspoonsful onto prepared cookie sheet 2 1/2 inches apart. Bake for 8 to 15 minutes, depending on size of cookie, until they spring back to touch. Remove to wire rack to cool.

Filling: Beat egg whites until stiff. Add shortening and vanilla extract; blend. Add milk and then add the sugar. Beat until smooth. Spread filling on the bottom side of one cookie; top with a second cookie bottom side down. Repeat with the remaining cookies and filling.