Preheat the oven to 350º Fahrenheit. Spray a 9x13 baking pan with cooking spray.
In the bowl of a stand mixer (or use a hand mixer), mix the cake mix, milk, eggs and oil for 2 minutes, scraping the sides of the bowl as needed.
Pour the cake batter into the prepared pan.
Bake for 21-26 minutes or until the center of the cake bounces back when you touch it.
Allow the cake to cool for 5 minutes, then poke holes all over the top of the cake using a long-tined fork or a skewer.
Mix the jello powder with the boiling water. Use a whisk to stir until the powder dissolves. Then mix in the cold water.
Pour the jello over the cake so that it soaks into the holes.
Allow the cake to cool for 1 hour in the refrigerator.
Spread lemon curd evenly over the top of the cake.
Then spread Cool Whip evenly on top of the lemon curd.
Decorate with lemon zest or sliced lemons.
Store in the refrigerator until serving.
The calories shown are based on the cake being cut into 15 pieces, with 1 serving being 1 slice of cake. Since different brands of ingredients have different nutritional information, the calories shown are just an estimate. **We are not dietitians and recommend you seek a nutritionist for exact nutritional information. The information in the nutrition box are calculated through a program and there is room for error. If you need an accurate count, I recommend running the ingredients through your favorite nutrition calculator.**