01 - Preheat oven to 350°F. Line a 9x13-inch baking pan with parchment paper, leaving an overhang for easy removal.
02 - In a medium bowl, whisk together all-purpose flour, cocoa powder, baking powder, and salt.
03 - In a large bowl, cream softened butter and granulated sugar with an electric mixer or whisk until light and fluffy. Beat in egg and vanilla extract until fully incorporated.
04 - Gradually add the dry ingredients into the wet mixture, mixing until a smooth dough forms.
05 - Reserve one third of the dough. Press the remaining dough evenly into the bottom of the prepared pan to create the crust.
06 - Roll out the reserved dough to 1/4-inch thickness. Use a bat-shaped cookie cutter to cut out bat shapes. Set the bat cookies aside.
07 - In a clean bowl, whisk together pumpkin purée, evaporated milk, eggs, packed light brown sugar, ground cinnamon, ground ginger, ground nutmeg, ground cloves, and salt until the mixture is smooth.
08 - Pour the pumpkin filling evenly over the crust. Arrange the bat-shaped cookies on the surface of the filling.
09 - Bake in preheated oven for 40 to 45 minutes, until the center is just set and a toothpick inserted comes out mostly clean.
10 - Cool completely in the pan on a wire rack. Lift bars from the pan using the parchment overhang. Cut into bars and dust with powdered sugar if desired.