Preheat Oven and Prepare Pans: Preheat your oven to 350°F (175°C). Grease and flour two 8-inch round cake pans or one 9×13-inch cake pan.

Drain Pineapple: Drain the can of crushed pineapple, making sure to reserve the juice in a separate container. Set aside both the drained pineapple and the reserved juice.

Make Cake Batter: In a large mixing bowl, combine the yellow cake mix, vegetable oil, 3/4 cup of the reserved pineapple juice, and the eggs. Beat with an electric mixer (hand mixer or stand mixer) on medium speed until well combined. Gently fold in the drained mandarin oranges.

Pour into Pans: Divide the batter evenly between the two prepared 8-inch round cake pans (or pour it all into the 9×13-inch pan).

Bake: Bake for 22-25 minutes (for 8-inch rounds) or 30-35 minutes (for 9×13-inch pan), or until a wooden toothpick inserted into the center comes out clean.

Cool Cake: Let the cake layers (or the single cake) cool in the pan(s) for about 10 minutes before inverting them onto wire racks to cool completely.

Make Frosting: In a medium bowl, combine the drained crushed pineapple (that you set aside earlier) and the dry instant vanilla pudding mix. Stir well. Gently fold in the thawed Cool Whip until everything is evenly combined.

Assemble Cake (if using round pans):

• Once the cake layers are completely cool, place one layer on a cake plate or serving platter.
• Spread about half of the frosting evenly over the top of the first layer.
• Carefully place the second cake layer on top of the frosting.
• Spread the remaining frosting over the top and sides of the cake.

Frost Cake (if using 9×13 pan): Once the cake is completely cool, spread the frosting evenly over the top of the cake directly in the pan.

Garnish (Optional): Garnish the cake with extra mandarin orange segments or pineapple chunks, if desired.

Chill and Serve: Chill the cake in the refrigerator for at least 1 hour before slicing and serving.