Preheat the oven to 350°F and generously grease and flour a bundt pan.
In a stand mixer, blend together butter, vegetable oil, both sugars, pumpkin puree, and vanilla extract until smooth at medium speed.
Incorporate eggs, pumpkin pie spice, and cinnamon, mixing until just combined.
In a separate bowl, sift flour, cornstarch, and baking soda, then slowly add to the mixer with salt on low speed until just combined.
Pour the batter into the prepared bundt pan and bake for 60 minutes, or until fully cooked.
While the cake is baking, create the topping by combining granulated sugar, pumpkin pie spice, and cinnamon in a medium bowl. Set aside.
Once baked, let the cake cool in the pan for ten minutes. Invert the pan onto a wire rack, placing a large jelly roll pan underneath to catch the sugar mixture.
While the cake is still warm, brush it with melted butter and generously sprinkle the sugar mixture on top. Enjoy the deliciousness!