Preheat oven to 350°. Line 2 rimmed baking sheets with parchment paper.
In a large bowl, whisk together flour, pumpkin pie spice, baking powder, salt, and baking soda until well combined.
In a medium bowl, whisk together brown sugar, pumpkin, milk, oil, and 1 teaspoon vanilla extract. Gradually whisk flour mixture into sugar mixture just until batter is smooth and combined.
Using a 1-tablespoon levered scoop, portion batter 1 inch apart onto prepared baking sheets. With a damp finger, smooth tops of batter portions.
Bake until golden brown and firm to the touch, 10 to 15 minutes. Let cool completely.
In another large bowl, beat together butter, cream cheese, and remaining ¼ teaspoon vanilla extract at low speed until smooth, scraping down sides as needed, approximately 1 minute. Gradually beat in confectioners’ sugar until fully incorporated before adding more. Increase speed to medium and beat until smooth. Reserve 3 tablespoons frosting. Transfer remaining frosting to a piping bag and cut a ½-inch opening from the tip. Pipe frosting onto flat side of 12 whoopie pies. Top with remaining whoopie pies, flat side down.
To reserved 3 tablespoons frosting, add enough food coloring to achieve desired green hue. Transfer green frosting to a small piping bag fitted with a small leaf tip (Wilton #352). Pipe 2 leaves on top of each whoopie pie. Change to a small round tip (Wilton #3), and pipe tendrils onto each whoopie pie. Place whoopie pies in an airtight container, refrigerate, and serve within 2 days.
Notes
*We used Wilton Juniper Green gel food coloring.
Recipe by TeaTime Magazine at https://teatimemagazine.com/petite-pumpkin-whoopie-pies/