Preheat oven to 350. Spray a 13″ x 9″ pan with non-stick cooking spray.
Prepare cake mix as directed on package, using eggs and oil and replacing the water with in the directions with orange juice.
Pour into prepared pan. Bake for 30-40 minutes until cake springs back when touched.
Remove the cake from the oven and allow it to cool completely (do not remove it from the pan)
Use a skewer to poke small holes all over the cake, piercing all the way to bottom.
In a bowl, combine Jell-O and boiling water and stir until gelatin is completely dissolved.
Add cold water and stir.
Slowly pour the Jell-O mixture over the entire cake.
-
Cover and chill for 2 hours.
Combine the pudding mix, milk and vanilla and beat well until the mixture starts to thicken.
Fold Cool Whip into the pudding mixture and use it to frost cake.
Cover and refrigerate for 4 hours.
Garnish with mandarin orange slices just before serving