Whoopie Pies with Balsamic Vinegar

Directions

1. Preheat oven to 350 degrees F. Position racks in the upper and lower thirds of the oven. Coat 2 large baking sheets with parchment paper and cooking spray.
2. Beat oil, brown sugar, egg and balsamic in a large bowl with an electric mixer on medium speed until combined. Whisk flour, cocoa, baking powder, baking soda and salt in a medium bowl. Gradually add the dry ingredients to the wet ingredients, alternating with milk, beat until smooth. Let the batter stand for 15 minutes. Drop batter by the tablespoonful onto the prepared baking sheets, spreading the batter into a 2- to 3-inch circle with the back of a spoon. Each large baking sheet accommodates 8 cookies, they will be close together. Bake the cookies until firm to the touch, about 8 minutes. Let cool on the baking sheet for 2 minutes, then transfer to a wire rack to cool completely. Repeat with the remaining batter.
3. Stir water and gelatin in a small heatproof cup or bowl. Let stand 1 minute. Bring 1/2 inch water to a gentle simmer in a small pan. Set the bowl with the gelatin mixture in the simmering water until the gelatin has dissolved completely. Stir the mixture until smooth. Let cool for 10 minutes. Beat cream, yogurt, sugar and balsamic in a medium bowl with an electric mixer on high speed until very thick, about 1 minute. With the mixer beating, add the gelatin mixture in a steady stream until well combined. Cover and refrigerate until the cream filling is thickened to the consistency of pudding, about 30 minutes. Whisk again.
4. Turn half the cookies bottom side up and top with a heaping tablespoon of the cream. Top with the remaining cookies. Chill in the refrigerator until the filling is set, about 30 minutes.