In the bowl of a stand mixer (or in a medium size mixing bowl if using a hand held mixer), add the butter and sugars. Using the paddle attachment, mix on medium speed until creamed together. This takes about 1 minute or so.
½ cup salted butter, ¼ cup granulated white sugar, ¼ cup packed brown sugar
Add the egg and vanilla paste (or extract) and blend until incorporated. This takes about 30 seconds.
1 large egg, 1 teaspoon vanilla paste or vanilla extract
In a bowl combine the flour, apple cider powdered mix, baking powder, salt and seasonings.
1¼ cups all-purpose flour, ½ teaspoon baking powder, ½ teaspoon ground cinnamon, ¼ teaspoon ground cloves, ¼ teaspoon ground nutmeg, 1 packet powdered apple cider mix, ½ teaspoon fine grind sea salt or kosher salt
Add the flour to the butter and sugar mixture and blend on low speed until incorporated. Scrape down the sides of the bowl as needed. The batter will be thick like peanut butter, but the applesauce will loosen it up. Add the applesauce and blend until incorporated.
4-5 Tablespoons unsweetened apple sauce
Line a baking tray with parchment. Using a cookie scoop, scoop out about 1 Tablespoon for smaller whoopie pie or 2 Tablespoons for larger whoopie pies, and drop the batter onto the prepared cookie sheet about 2" apart. Bake in a preheated oven at 350F for 10 minutes. The time does not change for the smaller or bigger cookies. When done, remove the cookies from the boven and transfer to a cooling rack to cool completely. Repeat for the remaining batter. You can use the same cookie sheet and parchment if you like, but the baking time may need to be shortened since the pan will be warm.
Making the Whoopie Pie Filling
Create a double boiler by filling a small pot with about 1" of water. Place a glass or metal mixing bowl on top of the pot so it is elevated above the water. Make sure the bottom of the bowl does not touch the water OR use a double boiler if you have one. *Make sure your mixing bowl is very clean and does not contain any fat residue or your egg whites won't whip up correctly.
Heat the water on high until it begins to boil and then turn the heat down to low or medium low to maintain a simmer. Place the egg whites and sugar in the mixing bowl and whisk to combine. Whisk the mixture every minute or so until it reaches 160℉/71℃. This will melt the sugar and pasteurize the egg whites. If the egg whites start to look like they are cooking, your heat is too high or your bowl is touching the water or you aren't whisking enough.
2 large egg whites, 6 Tablespoons granulated sugar
Once the egg white mixture reaches 160℉/71℃, remove the mixing bowl from the pot and turn off the stove. Pour the sugar and egg white mixture into the bowl of your stand mixer or you can use an electric hand mixer and use the same mixing bowl. Use the whisk attachment on a stand mixer and the regular beaters on a hand held mixer and whisk/beat the warm sugar and egg white mixture On HIGH speed until it forms stiff peaks. This can take up to 10-15 minutes, but usually only takes 5 minutes or so.
Once stiff peaks have formed, add the sifted powdered sugar and powdered apple cider mix to the bowl all at once and mix on low speed until incorporated. Then increase the speed to medium for about 30-60 seconds or until you have a smooth mixture.
⅔ cup sifted powdered sugar, 2 packets powdered apple cider
Add the Crisco and butter and whisk/beat on medium-high speed until you have a fluffy filling. Add the apple sauce and mix on low until combined.
¼ cup Crisco vegetable shortening, 10 Tablespoons salted butter, 2 Tablespoons apple sauce
Assembling the Whoopie Pies
Once the cookies have cooled, assemble them by spreading about 2 Tablespoons (use 4 Tablespoons if making the larger size) of the filling onto the bottom (flat side) of a cookie. Top with a second cookie. Repeat for all the whoopie pies.
Refrigerate for about 30 minutes prior to serving to firm the filling up.