Preheat the oven to 350°F and spray a 13x9-inch baking pan with cooking spray.
In a medium mixing bowl using an electric mixer, beat together cake mix, 1/2 melted butter and 1 large egg. Beat until fully moistened. Press the cake layer evenly into the bottom of the pan.
In the same bowl, whip together cream cheese, remaining 1/2 cup melted butter, lemon pudding mix and heavy cream. Beat just until creamy and no lumps remain.
Add 3 eggs one at a time, beating well after each addition.
Lower the speed of the mixer, and add the powdered sugar gradually. Whip until smooth and fluffy.
Pour the cream cheese mixture evenly over the crust, spread using an offset spatula.
Bake for 40-45 minutes. The center should still move when gently shaken.
Cool completely in the pan on a wire rack, then, slice into desired size pieces.
Dust the top of the cake with powdered sugar and serve topped with a dollop of whipped cream, if desired.