Whoopie Pies

Place 8 ounces cream cheese and 2 tablespoons unsalted butter in the bowl of a stand mixer (or large bowl if using an electric hand mixer). Beat with the paddle attachment on high speed until smooth and fluffy, scraping down the sides halfway through, 2 to 3 minutes total. Switch to the whisk attachment.

With the mixer on high speed, add 1 cup powdered sugar, 1/4 cup at a time, until incorporated, about 45 seconds per addition. Scrape down the sides after each addition of powdered sugar. Add 7 ounces marshmallow fluff or marshmallow creme, 1/2 teaspoon vanilla extract, and a pinch of kosher salt, and beat until combined, about 45 seconds more. Cover and refrigerate until firm, at least 1 hour. Meanwhile, make the cookies.

Place 1 stick unsalted butter in the bowl of a stand mixer (or large bowl if using an electric hand mixer). Let sit at room temperature until softened, about 1 hour.

Arrange 2 racks to divide the oven into thirds and heat the oven to 350°F. Line 2 baking sheets with parchment paper.

Place 1 3/4 cups all-purpose flour, 2/3 cup Dutch processed cocoa powder, and 1 teaspoon kosher salt in a medium bowl and whisk to combine.

If using instant coffee, place 1 cup buttermilk and 2 teaspoons instant coffee granules in a liquid measuring cup and whisk to combine. Place 1 large egg and 1 1/2 teaspoons vanilla extract in a second small bowl and whisk to combine.

Add 1 cup packed dark brown sugar and 1 1/4 teaspoons baking soda to the bowl of butter. Beat with the paddle attachment on high speed until light and fluffy, stopping and scraping down the sides of the bowl with a spatula halfway through, about 4 minutes total.

Add the egg and vanilla mixture. Beat on high speed until fluffy and pale, scraping down the bowl halfway through mixing, about 1 minute total. Add half of the flour mixture and half of the buttermilk mixture. Beat on the lowest speed until just incorporated, 25 to 30 seconds. Stop and scrape down the sides. Add the remaining buttermilk and flour mixtures and beat on the lowest speed until just incorporated, 25 to 30 seconds. Scrape down the sides and beat on the lowest speed for 30 seconds more.

Using a 2-tablespoon cookie scoop, drop the batter onto the baking sheets, spacing them about 2 inches apart, 12 per baking sheet. Bake until the tops of the cookies are spongy and bounce back when poked, 13 to 15 minutes. Immediately transfer the cookies to a wire rack and let cool completely, about 30 minutes. Meanwhile, bake the remaining batter.

To assemble, flip half of the cookies over. Distribute the filling evenly onto those halves with a small cookie scoop, a spoon, or a pastry bag. Close the sandwich cookies with a second cookie flat-side down.