Step 1: Prepare the Cake
Preheat your oven to 350°F (or as directed on your cake mix box). Grease a 9×13-inch baking pan or line it with parchment.

In a mixing bowl, prepare the cake mix according to package instructions, but substitute the water with milk or vanilla almond milk. Add in the orange zest for extra citrus flavor.

Mix until smooth, then pour the batter into the prepared baking pan. Bake according to package directions—usually about 28–32 minutes—until golden and a toothpick comes out clean.

Let the cake cool for about 10 minutes on a wire rack. You want it slightly warm but not hot for the next step.

Step 2: Infuse the Cake with Orange Flavor
Use a skewer, chopstick, or fork to poke holes all over the surface of the warm cake. This is how the Jello will soak in.

In a heatproof bowl, dissolve the orange Jello in boiling water. Stir until completely dissolved, then mix in the fresh orange juice.

Slowly pour the Jello mixture evenly over the entire cake. Let it seep into the holes and absorb into the crumb.

Place the cake in the refrigerator and chill for at least 3 hours to set the filling and deepen the flavor.

Step 3: Make the Frosting
In a large mixing bowl, beat the mandarin oranges (with juice) and vanilla pudding mix together until combined and slightly thickened.

Gently fold in the Cool Whip until light, fluffy, and smooth. If desired, you can pulse the mandarin oranges first in a blender for a finer texture.

Once the cake is fully chilled, spread the frosting evenly over the top. Use a spatula to smooth it out.

Refrigerate the cake for another 30 minutes before slicing and serving.