1️⃣ Prepare the Cake: Preheat the oven to 350°F (175°C). Grease, flour, and line 3 round cake pans with wax paper.
Combine the cake mix, oil, mandarin oranges with juice, sugar, and eggs in a large bowl. Mix at medium speed for 2 minutes until smooth.
Pour the batter evenly into the prepared pans. Bake at 350°F for 20 minutes, or until the center bounces back when touched.
Cool the cakes in the pans for 10 minutes, then remove and cool completely on a cooling rack.

2️⃣ Prepare the Icing: Drain the juice from the pineapple and set aside.
In a medium bowl, combine the pineapple with the instant vanilla pudding mix. Stir in the Cool Whip until smooth.
If the icing is too thick, add a bit of reserved pineapple juice to thin it to the desired consistency.

3️⃣ Assemble the Cake: Once the cakes are completely cooled, frost with the prepared icing.
Store the cake in the refrigerator. It’s best enjoyed the next day!