One Girl Cookies' Chocolate Whoopie Pies

Preheat oven to 350°. Line a rimmed baking sheet with parchment paper.

Whisk flour, cocoa powder, baking soda, and salt in a medium bowl; set aside.

Whisk eggs, oil, granulated sugar, brown sugar, yogurt, and vanilla in a large bowl until well combined. Gradually whisk in dry ingredients until just blended, carefully scraping down sides of bowl with a rubber spatula. The batter should be a bit stiff so it won’t spread very much when piped (test it—if it spreads, stir in 1–2 Tbsp. flour).

Using a pastry bag fitted with a large plain tip, pipe out 2" diameter rounds onto prepared baking sheet, leaving 1½" between them. Hold pastry bag completely vertical to help achieve nice rounds. If you have to wait between batches, keep batter refrigerated.

As soon as baking sheet is full, transfer to oven and bake whoopie pies until they spring back when touched, 8–10 minutes. Transfer to a wire rack; let cool completely.

Place cream cheese and butter in the bowl of a stand mixer fitted with the paddle attachment and beat on medium speed until light and fluffy, about 3 minutes. With motor running, add powdered sugar, ½ cup at a time, and beat and until pale and fluffy, scraping down sides of bowl as needed, about 5 minutes. Add vanilla and salt and mix on low speed until well blended.

Turn half of the cooled whoopie pies over so they are flat side up. Using an offset spatula, dollop a nickel-sized ball of frosting into the center of each and top with remaining pies.

Do Ahead: Vanilla filling can be stored up to 5 days in the refrigerator. Bring to room temperature before filling.