Preheat oven to 375 degrees. Line 2 baking sheets with parchment paper.
In a medium bowl, whisk together eggs, buttermilk, vanilla, applesauce, and apple pie spice until blended well.
In a mixing bowl for your electric mixer place flour, sugar, baking powder, salt, baking soda, butter, and shortening.
Add half of the egg mixture to the flour mixture and beat on medium speed for 2 minutes.
Add remaining liquid and beat for 2 additional minutes.
To place batter on baking sheets, use a 1/4 measuring cup. For large whoopie pies fill the cup and for smaller whoopee pies, only fill half way. Space the cookies leaving 2 inches in between. The batter should be like pancake batter and you can easily use your finger or back of a spoon to coax the batter into a near perfect circle.
Bake 8-12 minutes, until edges just begin to brown. Cool and then peel cakes from parchment paper.
For filling, place apple cider in a small saucepan and heat over medium-high heat until reduced to 1 tablespoon. Let cool.
Beat butter and cream cheese using an electric mixer. Gradually add confectioners' sugar. Mix in vanilla, cinnamon, allspice, and reduced apple cider.
Thin filling to desired consistency with half and half.
Turn whoopee cakes so bottom faces up. Spread filling on half of them. This is sometimes easier to do using a pastry bag. Top with the cookies that don't have filling to make sandwiches.