Chocolate Whoopie Pies with Cassis Filling

In a medium bowl, whisk together flour, cocoa powder, baking soda, and salt.

In the bowl of an electric mixer fitted with the paddle attachment, beat together sugars, yogurt, oil, eggs, and vanilla on medium speed for 3 minutes. Scrape down sides of bowl with a spatula. With the mixer on low, gradually add flour mixture, about 30 seconds. Scrape down sides of bowl again and transfer batter to refrigerator for 30 minutes.

Preheat oven to 350 degrees. Line a baking sheets with parchment paper.

Transfer batter to a pastry bag fitted with a large plain round tip (such as Ateco #809) and a large coupler. Pipe 2-inch circles onto prepared baking sheet, leaving 1 1/2 inches between each. Take care to keep your pastry bag completely vertical to make nice circles. If working in batches, keep batter refrigerated between each batch.

Transfer baking sheets to oven; bake until whoopie pies spring back when touched, 7 to 9 minutes. Remove from oven and let cool completely.

Fit a pastry bag with a large plain round tip (such as Ateco #809) and a large coupler; fill pastry bag with cassis filling. Turn half of the whoopies over so that they are bottom side up. Pipe a small dollop of cassis filling onto each whoopie bottom; sandwich with remaining whoopies.