From "Cake Mix Cookies" by Camilla V. Saulsbury
1 18.25-ounce package yellow cake mix
1 cup creamy peanut butter
2 large eggs
1/2 cup vegetable oil
2 cups semisweet chocolate chips
1 14-ounce can sweetened condensed milk
2 tablespoons butter
2 teaspoons vanilla extract
Preheat the oven to 350 degrees F. Position oven rack in middle of oven. Spray the bottom only of a 13 x 9-inch metal baking pan with nonstick cooking spray (I line with foil then spray).
In a large bowl place the cake mix, peanut butter, eggs and oil. Blend 1-2 minutes with an electric mixer set on low speed until well blended. Reserve 1-1/2 cups of the mixture. Press remaining mixture into bottom of prepared pan; set pan and reserved mixture aside.
Meanwhile, in a heavy saucepan set over low heat, melt the chocolate chips with the condensed milk and butter, stirring until blended and smooth. Remove from heat and stir in vanilla extract; pour over crust. Sprinkle with remaining crumb mixture.
Bake 20-25 minutes or until golden brown and topping is firm to the tough. Transfer to wire rack and cool completely; cut into bars.