Preheat oven to 350 degrees F. Lightly grease a 9x13" cake pan and set aside.
Prepare the cake mix according to package instructions and pour into the prepared cake pan. DO NOT BAKE, set aside.
Combine the 2 cups sugar, flour, eggs, lemon zest and lemon juice in a bowl and whisk together until sugar is dissolved. Pour over the prepared cake mix. Bake for 40 to 45 minutes, or until toothpick inserted in center comes out clean.
Let the cake cool completely before frosting! Whisk together the lemon pudding mix with the cold milk until smooth and thickened (about 2 minutes), then fold in the thawed Cool Whip, until fully combined.
Spread the frosting over the cake and enjoy right away or chill, covered, in the fridge until ready to serve. Enjoy!