Preheat the oven to 350 degrees. Prepare a 10.5 inch cast iron skillet with baking spray with flour. 

In a medium sized mixing bowl combine the cake mix and melted butter until crumbly. Remove 1 cup of the crumbs and set aside for later. 

Add the remaining ingredients to the cake mix and mix well. Some small lumps may remain. 

Pour the cake batter into the prepared skillet and top with the reserved crumbs. Bake at 350 degrees for 25-30 minutes or until a toothpick inserted near the center comes out clean. 

Serve warm with whipped cream or vanilla ice cream if desired.