Preheat the oven to 350 degrees F. Line a 9x13 baking dish with parchment paper. To secure the sides of the parchment paper, you can use metal binder clips.
In a large bowl, add the 15.25 ounce box yellow cake mix, melted ½ cup butter, and 1 large egg. Mix using a spatula until a thick dough forms.
Firmly and evenly press the dough into the bottom of the prepared baking dish. Set aside.
Pumpkin Filling
In a separate large bowl, add the 8 ounces cream cheese, 2 teaspoons. pumpkin pie spice, and 1 teaspoon vanilla extract. Beat using a hand mixer on medium speed until smooth.
Add the 15 ounces canned pumpkin puree and beat until well combined. Scrape down the sides and bottom of the bowl.
Add the melted ½ cup butter and 3 large eggs. Beat until the eggs are combined.
Add the 2 cups powdered sugar and mix on low until combined.
Pour the pumpkin filling over the crust dough in your pan. Evenly spread out.
Place in the preheated oven and bake for about 45 minutes. To test, give the bars a wiggle. The center of the bars should slightly jiggle when they’re done baking.
Allow the bars to cool completely.
Place in the fridge to chill1 hour before serving.
Cover with plastic wrap or store in an airtight container in the fridge.
Notes
Pumpkin Puree: Winter squash or sweet potatoes can be used instead of the pumpkin puree. Be sure to remove any excess liquid so it has the consistency of the canned pumpkin puree. Storage: Place in an airtight container and store in the fridge for up to 5 days.Freezing: Place the bars whole in the freezer until firm. Wrap tightly in 2 layers of plastic wrap, a layer of heavy-duty tin foil, and in a freezer bag for up to 2 months.