Prepare and bake cake mixes as directed. Pour into 1/2 sheet cake pan that has been greased and floured. Bake according to directions on box.
15 minutes before cake is finished baking, In a large sauce pan combine, milk, sugar, butter, and vanilla. Cook and stir over medium heat until the sugar is dissolved, then add corn starch that has been thinned by the above mixture and stir to completely dissolve, next add the coconut, chopped nuts, and powdered sugar and continue to stir for 5 minutes...lastly add the Hot Fudge topping and stir to completely incorporate without lumps. Turn off heat and wait until cake is fully cooked.
When cake is fully cooked, remove from oven and place pan on cooling rack...poke holes on the entire top of cake with fork, and pour cooked icing over the entire surface of the cake...careful not to burn yourself at this stage...icing will be very thin and will flow into and around the cake...it will look like a syrup at this stage...the coconut and nuts will sit on top of the cake and the cake will look very moist at this stage as well...set aside and let cake and icing cool completely...the icing will solidify and become very gooey. Enjoy.