Whoopie Pies (with spinach puree) Recipe from Jessica Seinfeld

Ingredients

• 1 cup all-purpose flour, spooned and leveled
• 1 cup whole-wheat pastry flour, spooned and leveled
• 1/2 cup unsweetened cocoa powder, spooned and leveled
• 1 teaspoon baking soda
• 1/2 teaspoon baking powder
• 1/4 teaspoon kosher salt
• 1/2 cup light olive oil
• 1 1/4 cups packed light brown sugar
• 2 large egg whites
• 1/2 cup spinach puree
• 2 teaspoons pure vanilla extract
• 1/2 cup low-fat buttermilk
• Nonstick vegetable cooking spray
• 1/2 cup (1 stick) unsalted butter, softened
• 1 1/4 cups confectioners’ sugar, spooned and leveled
• 2 cups marshmallow cream
• 1 teaspoon pure vanilla extract