01 - Preheat the oven to 350°F. Line two baking sheets with parchment paper to prevent sticking.
02 - In a medium bowl, whisk together all-purpose flour, baking powder, baking soda, salt, and pumpkin pie spice until evenly blended.
03 - In a large bowl, cream the softened butter and packed light brown sugar with an electric mixer until the mixture is light and fluffy.
04 - Beat in the eggs, one at a time, into the creamed mixture. Add canned pumpkin purée and vanilla extract, mixing until smooth.
05 - Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix.
06 - Using a tablespoon or small ice cream scoop, place portions of batter onto the prepared baking sheets, spacing each mound approximately 2 inches apart.
07 - Bake for 12 to 15 minutes or until the cookies are set and spring back when touched. Allow cookies to cool on the baking sheets for 5 minutes, then transfer to a wire rack to cool completely.
08 - While cookies cool, beat the softened butter and cream cheese with an electric mixer until smooth. Mix in powdered sugar, vanilla extract, and a pinch of salt. Continue beating until the filling is creamy and fluffy.
09 - If colored filling is desired, divide the mixture into separate bowls and blend in food coloring gels to achieve preferred shades.
10 - Spread or pipe a generous layer of filling onto the flat side of half the cooled cookies. Top with remaining cookies to form sandwiches.
11 - Decorate sandwiched cookies with candy eyes, chocolate chips, licorice, and sprinkles to create playful monster faces, using a little filling to adhere decorations as needed.
12 - Chill assembled whoopie pies for 15 minutes to allow decorations to set before serving.