Preheat oven to the temperature specified on the yellow cake mix box.

Grease and flour a 9x13 inch baking pan.

Prepare the yellow cake mix according to package directions or your own scratch recipe.

Pour the cake batter into the prepared pan.

Bake according to the directions on the cake mix box or until a toothpick inserted into the center comes out clean.

A few minutes before the cake is done, prepare the cinnamon sugar topping.

In a small bowl, mix cinnamon with confectioners' sugar.

Remove the cake from the oven and immediately sprinkle the cinnamon sugar mixture evenly over the top.

Cut the butter into small squares and place them evenly on top of the cinnamon sugar mixture.

Let the butter melt completely from the residual heat of the cake.

Allow the cake to cool completely in the pan.

Cut into squares and serve plain or with a scoop of your favorite ice cream.