Prepare the white cake according to the box directions. Allow the cake to cool completely.
Using a bamboo skewer, poke holes in the cake with about 1 inch between holes.
Add the orange gelatin mix into a small mixing bowl or a 2-cup measuring cup.
Stir in the boiling water. Continue stirring until the gelatin is completely dissolved.
Stir in the cold water. Continue stirring for 30 seconds to 1 minute.
Spoon, or pour, the gelatin into the holes in the cake.
Cover and chill in the refrigerator for 2 hours.
After the cake has chilled, add the instant vanilla pudding mix to a medium-sized mixing bowl.
Whisk in the milk. Continue whisking for about 1 minute until the pudding begins to thicken.
Fold in the whipped topping.
Evenly sprinkle the chopped mandarin oranges over the top of the cake.
Using a silicone spatula or an offset spatula, evenly spread the pudding mixture over the chopped mandarin oranges. Cover and chill in the refrigerator for 2 more hours.
Just before serving, add the 1½ cups of whipped topping to a disposable piping bag or a quart-size Ziploc with a corner snipped off.
Slice the 15 slices measuring 2½ inches by 3 inches each.
Gently squeeze out 15 silver dollar-sized dollops (about 1½ tablespoons each). Place 1 of the mandarin orange sections on each of the whipped topping dollops. Keep the cake refrigerated until ready to serve.
Notes
Oven temperatures vary and may need to be recalibrated periodically to ensure they are accurate. Make sure to check your cake at the lower end of the recommended baking time.
When pouring the jello into the holes of the cake, tap the pan on the counter a few times to get rid of any air bubbles, and make sure the jello fills the holes completely.
Make sure you don’t skip the chilling step. It’s important to give the jello and pudding time to set and soak into the cake before serving it.