Preheat oven to 350F degrees. Spray a 9x13-inch baking dish with nonstick cooking spray.

Drain the can of mandarin oranges, setting aside ½ cup of the juice (discard the rest of the juice).

For the cake: combine 1 box yellow cake mix, 1 stick unsalted butter (½ cup), ½ cup mandarin orange juice, 4 large eggs and 1 teaspoon vanilla extract. Beat for 3-4 minutes on medium-high.

Add drained 15 ounce can mandarin oranges and gently stir until combined (leaving some of the oranges chunky).

Spread batter into prepared baking dish and bake for about 25-30 minutes. Remove from oven and cool completely or until a toothpick inserted comes out clean (oven times can vary).

Drain the can of crushed pineapples very well, setting aside ¾ cups of the juice (discard the rest of the juice).

Once cake is cool, in a bowl, stir together ¾ cup juice from the crushed pineapple with 4 ounce box vanilla instant pudding mix.

Stir in ½ cup powdered sugar. Then fold in 4 ounces Cool Whip (whipped topping).

Finally, stir in drained 20 ounce can crushed pineapple. Note: if your frosting seems a bit too "liquidy" just add in a little more of the Cool Whip until you get a stiffer consistency.

Spread frosting on cooled cake. To help the frosting finish setting up, place cake into the refrigerator for at least 2-3 hours before slicing.

When cooled, slice cake into 12 pieces (while in the pan) and then top each slice with extra mandarin orange slices. Keep cake refrigerated.