Step 1

Preheat the oven to 350°F. In a large bowl, combine the cake mix, eggs and oil. Grease a 13x9-inch baking pan, and press two-thirds of the mixture into the pan in an even layer. Set the rest of the cake mix combination aside.

Step 2

In a microwave-safe bowl, combine the sweetened condensed milk, chocolate chips and butter. Microwave the mixture, uncovered, until the chips and the butter have melted, then stir to combine them thoroughly. The mixture should be smooth. Pour the mixture over the cake mix layer.

Step 3

Using a teaspoon, drop scoops of the remaining cake mix over the chocolate layer. Bake the bars until the top is lightly browned, 20 to 25 minutes. Let the bars cool before cutting them.