Preheat waffle iron. Sift together all dry ingredients in large bowl.
In another bowl, whisk together eggs, buttermilk and vanilla. Whisk in melted butter into buttermilk mixture, reserving 1 12/2 T. for later use.
Pour buttermilk mixture over the flour mixture and stir just until the dry ingredients are moistened,leaving it lumpy.
Brush both sides of waffle iron with reserve butter. Ladle a thin layer of batter over bottom of waffle iron. Arrange a layer of banana slices about 1/2 inch apart on top and then ladle another thin layer of batter over the slices, creating a banana sandwich. Cook until crisp and golden.