Preheat oven to 350 degrees and grease a casserole dish.
Combine all lemon cake ingredients in a bowl and stir until smooth. Pour into prepared pan and bake for 20-25 minutes or until an inserted toothpick comes out clean.
When the cake is done, use the back of a wooden spoon or butter knife to poke holes all over the cake. I leave about 3/4 or 1 inch between each hole.
Mix your instant pudding mix (keep out 1 teaspoon for the whipped topping) and cold milk together and then IMMEDIATELY pour over your cake so it can sink into the holes! Place cake in fridge until cake is cooled.
Beat heaving whipping cream with the teaspoon of instant pudding mix (this keeps it from "melting" during your party) and powdered sugar until stiff. Spread over cooled cake and top with lemon slices or berries!