Prepare the cake mix according to the box directions and bake in a 9 X 13" pan. Let cool.
Mix together the butter, sugar, cinnamon, vanilla, and condensed milk until smooth.
Poke 24 holes in the cooled white cake with the end of a wooden spoon.
Pour the milky cinnamon mixture over top of the cake, encouraging it to flow into the holes. Spread whipped topping over the cake.
Chill for 4 hours. Serve and enjoy!