FILLING
5 tbsp flour
1 cup milk
1 cup shortening - it will make your filling lighter and fluffier, but butter works as well
2-1/2 cups confectioner's sugar
dash salt
1 tsp vanilla
How to Make Chocolate Candy Bar Whoopie Pies
Whisk flour, baking soda, baking powder, baking soda, and cocoa in a medium bowl and set aside.
In the bowl of a stand mixer with the paddle attachment, cream together butter and sugar until light and fluffy
Add eggs and vanilla to the cream mixture, making sure to scrape the sides of the bowl as you mix it so it's fully combined.
Add the dry ingredients, alternating between milk and mix until just combined
Stir in the boiling water and mix on low until it looks glossy and smooth. It will look like cake batter and not cookie dough.
Place in the refrigerator for 30 mins-1 hour
Using a medium cookie scoop, drop the batter onto a parchment paper-lined baking sheet at least 2-3 inches apart.
Bake at 375 degrees for 8-11 minutes
Remove from oven and allow to fully cool
FILLING
Whisk 5 tbsp flour and 1 cup milk over low heat until it forms a thick paste - this will only take a couple of minutes, so be sure to vigorously whisk together, making sure all of the clumps are gone, and remove from heat as soon as it thickens up.
Remove paste from pan into a small bowl and allow to fully cool down
Mix 1 cup shortening or butter, powdered sugar, salt, and vanilla until well blended
Add cooled paste mixture and beat on high for 3-4 minutes or until light and fluffy, making sure all of the paste isn't stuck to the bottom of the bowl
Spread filling onto one of the cakes and top with a second cake to form a sandwich. Repeat with the rest.
Take the candy bar chunks and press them into the icing between the two cakes