• Preheat your oven to 350 degrees F. Grease a 9-inch x 13-inch baking dish and set aside.

Crust

• Reserve 1 cup of cake mix from the 15.25 ounces yellow cake mix and set it aside for the topping. Mix the remaining cake mix with 1 large egg and ½ cup melted butter with a rubber spatula until a dough forms. The crust may be very buttery - this is normal. Use the back of a metal spoon to spread the dough into the bottom of the prepared baking dish while pressing down firmly.
  
When making the crust, it may seem like there’s not enough dough for the pan, but just keep spreading it until the bottom is completely covered.

Filling

• Add 2 ¼ cups pumpkin puree, 2 ½ teaspoons pumpkin pie spice, 10 tablespoons light brown sugar, 2 large eggs, and ⅔ cup 2% milk to a large mixing bowl. Using a hand mixer, beat on low speed for 30 seconds. Then mix on medium speed until well combined, about 1-2 minutes. Pour the pumpkin filling on top of the crust layer and spread the filling out evenly.
  

Topping

• Add the reserved 1 cup yellow cake mix and ½ cup cold butter to a medium mixing bowl. Using a pastry cutter or fork, cut the butter into the cake mix until it has a sandy texture with tiny pieces of butter.
  
• Sprinkle the crumb mixture evenly over the pumpkin layer, covering it edge to edge.
  
• Bake for 50–55 minutes, until the crumb topping is deep golden brown. The pumpkin filling won’t be fully set when it comes out of the oven. That’s normal.
• Remove the cake from the oven and let it cool on a wire rack until it reaches room temperature, about 1 hour. Cover with plastic wrap and chill in the refrigerator for at least 1 hour.
  
• Top with whipped cream and chopped pecans, if desired, and then cut into 12 squares for serving.