Line two large baking sheets with parchment paper or a silicone baking mat.
In a medium bowl, whisk together flour, pumpkin spice, salt, baking powder, and baking soda.
In a separate large bowl using a hand mixer, beat the brown sugar, canola oil, 1/2 cup butter, pumpkin puree, eggs, and 1 teaspoon vanilla until smooth.
Fold the dry ingredients into the wet ingredients and stir until combined. The dough will very stick and soft.
Drop the dough onto prepared baking sheets using a tablespoon or medium cookie scoop leaving at least 2” between each cookie.
Bake the cookies for approximately 12-14 minutes or until they spring back when lightly pressed in the center.
Transfer cookies to a cooling rack with a spatula and allow to cool completely.
To make the filling, beat the remaining 1/2 cup butter and mascarpone in a large bowl until fluffy.
Slowly add powdered sugar 1 cup at a time beating well in between each addition.
Add the maple syrup and remaining 2 teaspoons vanilla and beat until fluffy.
Pipe the filling onto the bottoms of half of the cookies on the flat surface of the cookie.
Place the remaining cookies, flat side down, on top to create the sandwich.
Serve immediately or store in fridge in an airtight container for 2 to 3 days.
Notes
You can make the whoopie pies up to 3 days in advance and store in an airtight container in the refrigerator.