Step 1: Preheat and Prepare the Pan

Preheat oven to 350°F (175°C). Grease a 9×13-inch baking dish and set aside.

Step 2: Mix the Cake Batter

In a large mixing bowl, combine the vanilla cake mix, eggs, milk, vegetable oil, and orange zest. Beat with a mixer on medium speed for about 2 minutes until smooth and fully combined.

Step 3: Bake the Cake

Pour the batter evenly into the prepared baking dish. Bake according to the cake mix package directions, usually 28–32 minutes, or until a toothpick inserted in the center comes out clean.

Step 4: Prepare the Orange JELLO

While the cake is baking, place the orange JELLO powder into a heat-safe bowl. Carefully pour in the boiling water and whisk until the JELLO is completely dissolved. Stir in the fresh squeezed orange juice and set aside.

Step 5: Poke the Cake

Once the cake is removed from the oven, allow it to cool for about 10 minutes. Using the handle of a wooden spoon, poke holes evenly all over the cake, going about three-quarters of the way down.

Step 6: Add the JELLO Mixture

Slowly pour the prepared orange JELLO mixture evenly over the cake, making sure it fills the holes. Allow the cake to cool completely at room temperature, then refrigerate for at least 1 hour to set.

Step 7: Make the Frosting

In a blender or food processor, combine the undrained mandarin oranges and vanilla instant pudding mix. Blend until smooth and thickened.

Step 8: Fold in Cool Whip

Transfer the orange mixture to a bowl. Gently fold in the Cool Whip using a spatula until fully combined and fluffy.

Step 9: Frost the Cake

Spread the frosting evenly over the chilled cake. Cover and refrigerate for at least 2 additional hours before serving.