Preheat oven to 350°F (175°C).
Grease and flour a 9×13-inch baking pan.
Whisk together flour, cocoa powder, baking powder, baking soda, pumpkin pie spice, cinnamon, and salt.
In another bowl, beat eggs, granulated sugar, and brown sugar until smooth.
Mix in pumpkin puree.
Add vegetable oil.
Stir in milk.
Add vanilla extract.
Gradually fold the dry ingredients into the wet mixture.
Stir until just combined.
Fold in chocolate chips if using.
Pour batter evenly into the prepared pan.
Bake for 35–40 minutes or until a toothpick comes out clean.
Cool completely before frosting or serving.
Slice and enjoy.