Based on a recipe from The King Arthur Flour Cookie Companion cookbook. Since I live in Maine, where these are extrememly popular, I just had to try this recipe! I end up with a lot of marshmallow filling and I use it to make homemade marshmallows, often using a small cookie cutter to make them into shapes such as moose! They're a real hit in the hot chocolate when at camp and make great presents, particularly when presented alongside the whoopie pies themselves! The intro says, "These cookies are similar to the snack cake oatmeal pies -- two oatmeal cookies sandwiched around creme filling -- that you find at the grocery store. But instead of creme filling, we developed a rich, thick homemade marshmallow filling, which can be left plain, or flavored however you like (do we hear cinnamon?)."