1. Preheat the oven to 350 degrees F using an oven thermometer to ensure accuracy.

2. Grease a 9×13 inch cake pan with a pastry brush or paper towel coated with vegetable oil.

3. In a large mixing bowl, combine the cake mix, 1 cup of cold water, 1/2 cup of vegetable oil, and 3 large eggs. Use an electric hand mixer on low speed to mix the ingredients.

4. Scrape down the sides of the bowl with a silicone spatula to ensure all ingredients are incorporated. Then, beat the mixture on medium speed for 2 minutes.

5. Pour the cake batter into the prepared 9×13 inch cake pan. Use a silicone spatula to spread the batter evenly across the pan.

6. Bake the cake in the preheated oven for 23 minutes. Check for doneness by inserting a toothpick into the center; it should come out clean.

7. Allow the cake to cool on a wire cooling rack on the counter for about 20 minutes.

8. In a microwave-safe glass measuring cup, bring 1 cup of water to a boil in the microwave.

9. In a small bowl, combine the orange Jello with the boiling water. Use a whisk to stir until all the Jello is fully dissolved.

10. Use a metal chopstick or the end of a wooden spoon to poke holes about 1 inch apart across the top of the cooled cake.

11. Slowly pour the liquid orange Jello evenly over the top of the cake, ensuring it seeps into the holes. Let the cake cool and absorb the Jello for about 30 minutes.

12. In a clean large mixing bowl, combine the vanilla instant pudding and 1 cup of cold milk. Use a whisk to mix for about 1 minute until smooth.

13. Add the Cool Whip and vanilla extract to the pudding mixture. Use the whisk to blend until the frosting is smooth and well combined.

14. Use an offset spatula to evenly spread the frosting over the top of the cake.

15. Place the cake in the refrigerator for about 1 hour to set before slicing.

16. Use a sharp chef’s knife to slice the cake into 12 even pieces. Serve each slice with a mandarin orange on top.