Whoopie Pie

Ingredients

• 1 3/4 cups all purpose flour 210g
• 3/4 cup unsalted butter 170g, room temperature
• 1 cup sugar
• 2/3 cup cocoa powder
• 1/2 teaspoon salt
• 1 teaspoon baking powder
• 1/4 teaspoon baking soda
• 1 egg large, room temperature
• 1/4 cup buttermilk
• 1/4 cup coffee
• 1/4 cup cream Bailey's Original Irish
• 5 egg whites at room temperature
• 2 cups unsalted butter 452g, at room temperature
• 1 2/3 cups granulated sugar 333g
• 1/4 teaspoon salt
• 1 teaspoon vanilla extract
• 3 tablespoons cream Bailey's Original Irish, Plus more to taste