Step 1

Bake cake according to package directions in 2 cake pans. Cool.

Step 2

When cool, slice each layer in half horizontally, making 4 layers.

Step 3

In a medium mixing bowl, combine sweetened condensed milk, lemon juice and lemon zest. Reserve half of mixture and set aside.

Step 4

Using half of the lemon milk mixture, pour between each cake layer.

Step 5

Gently fold the whipped topping into reserved lemon milk mixture. Using this as the frosting, frost the entire cake.

Step 6

Chill overnight in the refrigerator before serving.