Preheat your oven to 350°F. Grease and line an 8x8-inch baking dish with parchment paper, leaving some overhang for easy removal.
In a medium bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, nutmeg, and pumpkin pie spice. Set aside.
In a large bowl, whisk together the melted butter, pumpkin puree, granulated sugar, brown sugar, eggs, vanilla extract, and milk. Mix until smooth and well combined.
Gradually add the dry ingredients to the wet mixture, stirring gently with a spatula until just combined. Be careful not to overmix, as this can make the cake dense.
Pour the batter into the prepared baking dish and spread it out evenly with a spatula.
In a small bowl, mix the granulated sugar and cinnamon together. Sprinkle this mixture evenly over the top of the batter.
Bake for 25-30 minutes or until a toothpick inserted into the center comes out clean or with just a few moist crumbs. The edges should be slightly golden, and the cake should spring back when lightly pressed.
Allow the cake to cool in the pan on a wire rack for 10-15 minutes. Use the parchment overhang to lift the cake out of the pan, transfer it to a cutting board, and slice into squares.
