For the Whoopie Pies: Combine the ground flax with the hot water and whisk to a paste, let stand for at least 5 minutes to thicken

Combine the oil, mashed banana, sugar, vanilla extract and flax paste together in a large mixing bowl with a hand whisk.

Sift together the flour, spices, baking powder, baking soda and salt and add to the wet mixture, whisk until smooth.

Preheat the oven to 350°F and while you wait - refrigerate the batter

Scoop the batter onto a parchment paper lined sheet pan with a 1½ ounce scoop spaced 2" apart and bake for approximately 12-15 minutes or until lightly golden brown.

They will be puffed and springy when you press the centers..

Cool completely before filling with the peanut butter buttercream recipe follows.

For the Peanut Butter Filling: Combine all the ingredients for the peanut butter filling together except for the buttercream.

Cream it all smooth by hand with a spatula or with a mixer.

Add the optional buttercream last