In a large bowl, combine flour, white sugar, cocoa powder, 3/4 teaspoon salt, and baking powder. Stir in 1 1/2 cups milk, eggs, 1 1/2 teaspoons vanilla, and shortening.
Mix until smooth using an electric mixer. Drop batter by rounded teaspoons onto ungreased cookie sheets. Leave space, and only use a teaspoon; these spread.
Bake in preheated oven for 7 to 8 minutes.
Remove from pan immediately, and cool on wire rack.
To make the filling, combine the butter, confectioners' sugar, 1/8 teaspoon salt, marshmallow creme, 1 1/2 teaspoons vanilla, and 1 tablespoon milk in a medium bowl. Beat with mixer until fluffy.
Spread filling on one cookie, and top with another sandwich style.
