Preheat oven to 350 degrees F (175 degrees C).

Spray or grease a 9x13 inch pan.

In a large bowl, combine the yellow cake mix (reserving 1 cup for later), beaten egg, and melted butter.

Mix well until a dough forms.

Press the dough evenly into the prepared pan to create the crust.

In a separate bowl, beat together the pumpkin puree, beaten eggs, white sugar, brown sugar, and ground cinnamon until well combined.

Pour the pumpkin mixture evenly over the prepared crust.

In a small bowl, combine the reserved cup of yellow cake mix, sugar, and softened butter.

Use your fingers to crumble the mixture over the pumpkin filling.

If desired, add chopped nuts over the crumb topping.

Bake in the preheated oven for 40 to 45 minutes, or until a toothpick inserted into the center comes out clean.

Let cool completely before slicing and serving.