Preheat oven to 375°F. Cream butter and sugar. Add egg, vanilla, molasses, and maple syrup; beat well. Add sifted dry ingredients, and mix well. Drop by teaspoonful onto baking sheet. Bake 10 to 12 minutes.
Make filling: Cream together butter and sugar, beating until pale and fluffy. Add marshmallow fluff and vanilla and maple extracts; continue mixing until well blended. Let cookies cool completely before sandwiching two around a dollop of the filling.