Aunt Addie's Pumpkin Pie Dessert Squares

They say that this year, 2015, we will have a shortage of canned pumpkin on the grocery store shelves. In Illinois, where nearly 90% of  sugar pumpkins are grown, a wet growing season has resulted in a small harvest. So, if you see canned pumpkin in the grocery store, buy it now because they say it will be gone before Thanksgiving this year.
And if you find some, this is the recipe to make. If you knew my Aunt Addie, you would already know that this is good.

Ingredients for Base

1 package yellow cake mix
1/2 cup unsalted butter, melted
1 egg

Ingredients for Filling

1 16-ounce can pumpkin
1/2 cup brown sugar
2 1/2 teaspoon pumpkin pie spice
2 eggs
2/3 cup milk

Ingredients for Topping

1 cup reserved cake mix
1/4 cup sugar
1 teaspoon cinnamon
1/4 cup unsalted butter, softened

Instructions

Grease bottom only of 9x13 inch pan.
Reserve one cup of cake mix. Combine remaining mix with melted butter and egg. Press into pan.
Combine filling ingredients with mixer until smooth. Pour over crust.
Combine topping ingredients and sprinkle over pumpkin layer.
Bake at 350 degrees for 45-50 minutes or until knife inserted in center comes out clean.

Serve with whipped topping, if desired.