Preheat oven to 350 degrees.

Pour cake mix and pumpkin pie spice into a large bowl and stir. Add melted butter, egg, vanilla, and pumpkin puree. Mix until combined (dough will be thick).

Drop cookies by rounded Tablespoons onto a cookie sheet lined with parchment paper (for a smooth cookie surface when baked, make sure the cookie dough balls are smooth on top before placing in the oven).

Bake for about 12-13 minutes, or until cookies look set (barely golden brown, and do not look doughy in the centers). Whoopie pies are traditionally a soft-baked cookie with a cake-like texture, thus you don't want to over bake them.

Allow cookies to cool completely.

Cream butter and cream cheese together, until well combined, about 1-2 minutes. Add in vanilla and cinnamon. Mix. Add in powdered sugar, and mix until well combined.

With a spoon or a piping bag with a circular tip, add about 1 Tbsp (more or less, depending upon your preference) of filling to half of the cookies. Top with the other halves.

Enjoy!

For best results, store leftovers in the fridge.