01 - Preheat oven to 350°F. Line a 9x13-inch baking pan with parchment paper, extending an overhang for easy removal.
02 - In a medium bowl, whisk together flour, cocoa powder, baking powder, and salt for the cookie crust.
03 - In a large bowl, beat unsalted butter and granulated sugar with an electric mixer until light and fluffy. Blend in egg and vanilla extract.
04 - Gradually add dry ingredients to the butter mixture, mixing until a soft dough forms.
05 - Reserve 1/3 of the dough. Press the remainder evenly into the prepared pan to form the base layer.
06 - Roll reserved dough to 1/4-inch thickness. Cut out bat shapes using a small bat-shaped cookie cutter. Set aside.
07 - In a separate bowl, whisk together pumpkin purée, evaporated milk, eggs, packed brown sugar, cinnamon, ginger, nutmeg, cloves, and salt until the mixture is smooth and homogeneous.
08 - Pour pumpkin filling over the crust base and spread evenly. Place bat cookie cutouts on top of the filling.
09 - Transfer pan to oven and bake for 40 to 45 minutes, until the filling is just set and a toothpick inserted in the center comes out mostly clean.
10 - Allow to cool completely in the pan on a wire rack. Lift bars out using parchment overhang and cut into individual portions. Dust with powdered sugar if desired.