Root Beer Whoppie Pies

Name: Root Beer Whoppie Pies
Ingredients: 2-1/4 cups all-purpose flour; 1-1/2 teaspoons baking powder; 1/2 teaspoon salt; 4 tablespoons unsalted butter, at room temperature; 4 tablespoons vegetable shortening; 1/2 cup granulated sugar; 1/2 cup brown sugar; 2 large eggs; 1/2 cup buttermilk; 2 tablespoons milk; 1 teaspoon baking soda; 1 teaspoon white vinegar; 1 teaspoon root beer extract; 1-1/2 cups Marshmallow Fluff; 1-1/4 cups vegetable shortening; 1 cup confectioners sugar; 1 tablespoon root beer extract