Preheat oven to 350°F. Line two baking sheets with parchment paper.
In a large bowl whisk together the brown sugar, oil, pumpkin, egg, and vanilla until well combined.
Whisk together the flour, baking powder, baking soda, salt, ground cinnamon and pumpkin pie spice. Add the dry ingredients to the wet ingredients and mix well.
Using an ice cream scoop or tablespoon, drop evenly sized scoops of batter onto the prepared cookie sheets 2 inches apart each, making 16 scoops total.
Bake 10-15 minutes, until the cakes are springy. Let cool completely.
Filling
Beat cream cheese, butter, and salt until smooth. Add confectioners' sugar and vanilla extract and continue beating until smooth. Chill filling until it holds its shape, about 30 minutes.
Spread one tablespoon of filling onto the flat side of one cookie, top with another cookie. Repeat until you have 8 whoopie pies.