Prepare cake according to package directions for a 8 inch layer cake. After baking let cake cool 15 minutes.
While cake is cooling add jello to 1 cup boiling water and completely dissolve. Add 1/4 cup cold water.
With a fork. poke holes in both cakes. Slowly pour jello over each cake. Refridgerate in cake pans for at least 3 hours.
When Jello is set, remove 1 cake from pan. If cake does not remove easily put pan warm water for several minutes.
Spread cherry pie filling in on top of 1st layer. Loosen 2nd cake and put on top on pie filling. Using Cool Whip as frosting frost cake. when completely frosted drizzle hot fudge sauce over top of cake. If you wish you can garnish middle of frosted cake with a few cherries from remaining pie filling.