Preheat oven to 350 degrees. Grease and line a sheet pan.
In a medium bowl, whisk together cake flour, baking powder, baking soda, and salt.
In a large bowl, beat butter and cream cheese until smooth and fluffy (2 minutes).
Gradually add sugar and beat until light in color and texture.
Beat in eggs, one at a time, mixing well after each addition.
Stir in lemon zest, lemon juice, lemonade powder and vanilla extract.
Add the dry ingredients to the wet ingredients in 3 parts, alternating with the milk in 2 parts (begin and end with flour). Mix until just combined—don’t overmix.
Pour into prepared pan and smooth the top.
Bake for 25-30 minutes, or until a toothpick comes out clean from the center.
Cool cake completely.
While cake is cooling prepare frosting-
In a mixing bowl, mix pudding mix, powdered sugar, whole milk, and vanilla extract. Beat with an electric mixer until mixture has thickened, about 2-3 minutes.
Fold in cool whip until fully incorporated.
Spread evenly over cake. Garnish with lemon zest if you choose.
Chill cake for 1 hour before serving.