Root Beer Float Whoopie Pies

For the Vanilla Bean Cakes:

Position a rack in the center of the oven and preheat the oven to 375°F. Line two baking sheets with parchment paper.

Whisk together the flour, baking powder and salt and set aside.

In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter, and both sugars until light and fluffy. Add the eggs and buttermilk and beat until combined. The mixture will look curdled at this point, but that’s perfectly fine. It will smooth out in the next step.

In a measuring cup, combine the milk, baking soda, and vinegar. The mixture will foam and thicken. Add the milk mixture to the batter along with the flour mixture and beat on low until just combined. Add the vanilla bean paste and vanilla extract and beat on medium for about 2 minutes or until completely combined.

Using a small cookie scoop, drop 1 tablespoon sized scoops of batter onto the prepared baking sheets, spacing them at least 2 inches apart. Bake one sheet at a time for 9-10 minutes or until the edges of the cakes begin to brown. Remove from the oven and transfer to a wire rack to cool completely before filling.

For the Root Beer Swiss Meringue Buttercream:

Whisk the egg whites and sugar together in the bowl of your stand mixer or another bowl that’s heat proof. Place bowl over a pot of simmering water (double-boiler style) and whisk constantly until sugar is dissolved. It takes about 5 minutes. You can test whether the sugar is dissolved by sticking your finger in the mixture and seeing if it’s grainy or not. When it’s no longer grainy remove the bowl from the double boiler.

Beat on high speed using your stand mixer or an electric hand mixer for 10-15 minutes, or until the egg white mixture has turned into meringue and has increased in volume and is marshmallowy and glossy. The bottom of the bowl should be room temperature by this time.

At this point start adding the slices of butter, 1 tablespoon at a time. Wait until the butter is incorporated before adding more. If it helps, count to 15 between adding pieces of the butter.

Once all the butter is added, add the root beer flavoring. If the mixture gets runny at this point put the bowl in the fridge for 10-15 minutes. Then remove it from the fridge and begin whipping again. It will thicken up. If it gets curdled-looking, just keep whipping and it will smooth out.

Add the ground root beer candies to taste.

To Assemble:

Match the vanilla whoopie cakes up by size. Fill your piping bag with the filling mixture and pipe it onto the flat side of half of the whoopie pies. Top with another cake (top side out) and press together. To keep the pies fresh for up to 3 days, wrap each whoopie pie individually in plastic wrap.