Easy cake mix fudge bars are rich, gooey, chocolaty, and delicious. Some people call them "can't leave alone bars" and it is for good reason, you will want to keep going back for more.
In a mixing bowl, combine cake mix, oil, and eggs. Stir until uniform.
Place about 2/3 of the cake mix dough into the prepared pan and press to form a thin crust on the bottom of the pan.
Melt the butter in a medium glass mixing bowl in the microwave. Add the chocolate chips, peanut butter chips, and condensed milk.
Microwave on high in 20-30 second spurts, until you can stir the mixture smooth.
Pour the fudge mixture over the crust in the pan. Spread to form an even layer.
Drop small spoonsful of the remaining cake mix dough over the fudge layer. It won't be enough to cover all of the fudge, so just try to get it somewhat evenly distributed.
Bake for 25-30 minutes or until the cake parts of the bars look golden brown and cooked through.
Cool completely before cutting into bars and serving.