1. Pre-heat your oven to 375 degrees. Line a couple of baking sheets with parchment paper. 

   First, sift together your flour, cocoa powder, salt, and baking soda. In a separate bowl, whisk together whole milk and sour cream. Set both mixture aside.

   Then, in a stand mixer or with a hand mixer, cream the butter with your brown and granulated sugar for about 3 minutes, until fluffy and paled. 

   Then add your eggs and vanilla, beating on medium speed for another 2 minutes. Next, add half of the sifted dry ingredients. 

   Turn mixer to lowest speed and mix the dry ingredients in. Then add in your sour cream and milk mixture. Finish with the rest of the dry ingredients.

   Once your Chocolate Whoopie Pie Batter is prepared, use a tablespoon sized cookie scoop to distribute 8 mounds onto each baking sheet. Bake for approximately 9-11 minutes until they have baked through.

   Then allow the chocolate whoopie pies to cool completely before moving on to the Bailey’s Swiss Meringue Buttercream.

Bailey's Swiss Meringue Buttercream

1. First, separate 3 eggs and reserve the yolks for Lemon Bars or Banana Split Trifle. It is important that you don’t get even a drop of egg yolks into the egg whites.

   *For this step, Use a heatproof bowl set over barely simmering water. Do not let this submerge into water. 

   Once your egg whites are in your bowl, begin whisking the egg whites and sugar over the water and continue until the sugar dissolves, about 3-4 minutes later. 

   To ensure they are ready, dip one clean finger into the mixture. It should be hot and smooth without any of the sugar granules. If you prefer to use a thermometer, the temperature should be 160 degrees.

   Then the egg whites need to be whipped. So use your stand mixer with the whipping attachment, and use the speed of 8. Allow the whites to beat until the bowl is no longer warm to the touch. Let it beat for about 5-7 minutes.

   Meanwhile, cut up your room temperature butter into chunks. Butter should be soft but still a bit firm. I go with 2 tablespoon slices.

   Then begin adding the chunks of butter one at a time, giving it time to incorporate into meringue. Continue until all of your butter is gone. The mixture may look curdled after a minute. But let it keep going and it will turn into the silkiest, lightest frosting EVER. Once it is smooth, add in your Baileys and let it finish mixing to silky bliss.

   Once your Irish Cream Swiss Meringue Buttercream is ready, fill up a piping bag. Take a chocolate cookie and pipe in a generous swirl. Then sandwich it with a second cookie.