Preheat your oven to 325 degrees Fahrenheit (163 degrees Celsius).

Grease a 9x13-inch baking dish with nonstick spray, ensuring even coverage.

In a mixing bowl, combine the contents of the white cake mix box and the 15 oz. can of pure pumpkin.

Stir the mixture until it reaches a thick and well-combined consistency.

Transfer the pumpkin and cake mix mixture to the prepared baking dish.

Spread the mixture evenly in the dish.

Bake in the preheated oven at 325 F for approximately 25-30 minutes, or until a toothpick inserted into the center of the cake comes out clean.

While the base is baking, prepare the crumb topping.

In a mixing bowl, combine 2 cups of flour, sugar, sliced cold butter, vanilla extract, and cinnamon.

Use your hands or a pastry cutter to work the mixture until pea-sized crumbly balls form.

Once the base is fully baked, allow it to cool for about 10-15 minutes.

Sprinkle the crumb topping evenly over the cooled base.

Place the baking dish back into the oven at 325 F for an additional 10-15 minutes.

The crumb topping should turn golden brown and crisp during this final baking step.

Once done, remove the Pumpkin Crumb Cake from the oven and let it cool slightly.

Slice the cake into delicious servings and savor the delightful blend of flavors and textures.