2 cups all-purpose flour
1/2 cup Dutch-process cocoa powder
1 1/4 teaspoons baking soda
1 teaspoon salt
1 cup milk
1 teaspoon vanilla
1/4 cup unsalted butter, softened
1/4 cup applesauce
1 cup packed brown sugar
1 large egg
For filling
1 stick (1/2 cup) unsalted butter, softened
1 1/4 cups confectioners sugar
2 cups Marshmallow Fluff
1 teaspoon vanilla
Preheat oven to 350°F.
Whisk together flour, cocoa, baking soda and salt in a bowl until combined.
Stir together milk and vanilla in a small bowl.
Beat together butter, apple sauce and brown sugar in a large bowl with an electric mixer at medium-high speed until pale and fluffy.
Add egg, beating until combined.
Reduce speed to low and alternately mix in flour mixture and milk in batches and mixing until smooth.
Spoon 1/4-cup mounds of batter about 2 inches apart onto 2 parchment lined baking sheets.
Bake until tops are puffed and cakes spring back when touched, about 11 to 13 minutes.
Transfer with a metal spatula to a rack to cool completely.
Beat together butter, confectioners sugar, marshmallow and vanilla with electric mixer at medium speed until smooth, about 3 minutes.
Spread a rounded tablespoon filling on flat sides of half of cakes and top with remaining cakes.