1 pkg white cake mix (yellow works just as well if that is what you have)
1/3 C vegetable oil
1 (14 oz) can sweetened condensed milk
1 C semisweet chocolate chips
1/4 C butter
Preheat oven to 350 degrees.
In a large bowl, combine cake mix, eggs and oil.
Press 2/3 of mixture into a lightly greased (cooking spray) 9x13 pan; set aside.
In a microwave safe bowl, combine condensed milk, chocolate chips and butter.
Microwave, uncovered, for 45 seconds.
Stir and microwave for 45-60 seconds longer, or until chocolate chips and butter are melted.
Stir until smooth.
Pour over cake mixture in pan.
Sprinkle with remaining cake mixture over top.
Bake for 20-25 minutes, or until lightly browned.
Cool before serving.