Classic Whoopie Pies

Ingredients

• 1 cup unsalted butter, softened
• 2 cups granulated sugar
• 2 large eggs
• 2 teaspoons vanilla extract
• 4 cups all-purpose flour
• 1 cup unsweetened cocoa powder
• 1 1/2 teaspoons baking soda
• 1/2 teaspoon salt
• 1 cup buttermilk
• 1/2 cup hot water
• 1 cup heavy cream
• 2 cups confectioners' sugar
• 1 teaspoon vanilla extract