Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper.

In a medium bowl, whisk together the all-purpose flour, baking soda, baking powder, pumpkin pie spice, and salt.

In a separate large bowl, whisk the pumpkin puree, vegetable oil, brown sugar, egg, and vanilla extract until smooth.

Gently fold the dry ingredients into the wet ingredients until just combined. Be careful not to overmix.

Drop rounded tablespoons of the batter onto the prepared baking sheets, spacing each about 2 inches apart.

Bake in the preheated oven for 10 to 12 minutes, or until the tops spring back lightly when touched.

Let the cookies cool completely on wire racks.

Beat the softened cream cheese and butter together until smooth.

Gradually add the powdered sugar, beating until light and fluffy.

Spread or pipe about 2 tablespoons of filling onto the flat side of one cookie, then sandwich with another cookie.

Store assembled whoopie pies in an airtight container in the refrigerator.