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1
Cookies:
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2
Preheat oven to 375 F. Line two baking sheets with parchment paper.
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3
In a medium bowl, whisk the flour, baking powder and salt together. In the bowl of a stand mixer fitted with the paddle attachment, cream the butter, shortening and both sugars on medium speed until light and fluffy, about 3-4 minutes. Add the eggs and buttermilk and beat until combined (your batter may look curdled - mine definitely did, but it came together when I added the flour).
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4
Combine the milk, baking soda, and vinegar in a small measuring cup. With the mixer on low add half of the flour mixture, followed by the milk mixture and then the rest of the flour mixture. Beat just until everything is combined. Add the seeds from the vanilla bean and beat for another minute, until everything is completely combined.
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5
Using a small cookie scoop, drop the dough onto the prepared baking sheets, leaving about 2 inches of space between cookies. Bake the cookies, one sheet at a time, for 8-10 minutes, or until they are set and just beginning to brown. Let the cookies cool on the baking sheets for a few minutes before transferring to a wire rack to cool completely.
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6
Prepare the filling with the recipe below. Fill a pastry bag fitted with a plain round tip with the Nutella buttercream. Once the cookies are cool, pair them by size. Pipe some of the buttercream on the flat side of one cookie in each pair. Sandwich the whoopie pies together, pressing to nudge the filling to the edges.
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7
Filling:
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8
In the bowl of a stand mixer fitted with the paddle attachment, beat the butter and Nutella together until combined. Add the vanilla, milk and confectioners' sugar to the mixer bowl and beat on low speed until the powdered sugar is just about incorporated. Increase the mixer speed to medium and beat until the frosting is smooth.
