Prepare and bake the cake according to package directions, using a 13x9 inch cake pan. Let the cake cool for 15-20 minutes. Using a meat fork, skewer, or opposite end of a wooden spoon, poke holes in the cake every 1/2 inch to 1 inch.
Empty the gelatin into a medium-sized bowl and add the boiling water. Stir briskly for 2 minutes or until the gelatin is dissolved. Mix in the cold water. Evenly pour the gelatin over the poked cake. Place the covered cake in the refrigerator for 2-4 hours or until the gelatin is set.
Microwave the hot fudge topping in a microwave-safe container for 20-30 seconds, or until it is easy to pour. Drizzle the topping over the cake. Use the back of a spoon to spread it evenly. Allow the topping to cool if it is warm.
Frost the cake with the whipped topping.
Garnish with raspberries and chocolate shavings, if desired.
Store covered in the refrigerator.