• Preheat oven to 375 degrees.
• Line the two cookie sheets with parchment paper.

Whoopie Pies:

• Add the flour, cocoa powder, baking soda, and salt to a medium bowl.
• Whisk to blend together. Set aside.
• Add butter, vegetable oil, and brown sugar in a large mixing with a paddle attachment.
• Set on low speed, beat the butter, shortening, and brown sugar until combined.
• Continue beating while increasing the mixing speed to medium.
• Beat for 3 minutes. (Until fluffy and smooth.)
• While beating for another two minutes add in the egg and vanilla extract.
• Divide the dry mixture in half.
• Reduce the mixing speed to low, add one half of the flour and one half of the milk until completely mixed.
• Use a rubber spatula to scrape down the sides of the bowl.
• Add the rest of the flour and milk, beating until all ingredients are completely mixed.
• With a #70 cookie scoop (or a tablespoon) to measure the size of the cookie balls.
• Place each dough ball three inches apart on the prepared cookie sheets, baking one cookie sheet at a time.
• Bake at 375 degrees for 10 minutes.
• Allow the cookies to cool on the cookie sheets for 5 minutes.
• Transfer the cooled cookies to a cooling rack.
• Set aside the cooling rack until the cookies cool completely.

Filling:

• Add powdered sugar and butter in a mixing bowl with an electric mixer with a paddle attachment.
• Start on low and slowly increase the speed to medium for one minute.
• Increase the speed to high, adding in the heavy cream, vanilla, peppermint extract, and salt for 3 minutes.

Building the Whoopie Pie:

• Flip each half of the whoopie pies so the flat side is facing up.
• Add a large round tip to a pastry bag.
• Fill a pastry bag with filling.
• With the filling, start on the outside edge and work in a circle inward to the center.
• Place the second half of the whoopie pie, flat side down, on top of the filling.
• Repeat with the rest of the whoopie pies.
• Drizzle left with the melted chocolate chips and garnish with crushed peppermint