Preheat oven to 350 degrees F. Line a 13x9" baking pan with foil, extending the sides of the foil over the edges of the pan. Spray the foil liberally with cooking spray and set aside.

In a large bowl, combine the yellow cake mix, one (1) cup of the peanut butter, the egg and the oil with a rubber spatula or spoon until a thick dough comes together. Make sure to fully incorporate that peanut butter! Press the mixture evenly into the prepared pan and bake for 10 minutes. Meanwhile, mix together the remaining peanut butter, vanilla and condensed milk together.

Remove the pan from the oven and pour/spread the sweetened condensed milk mixture over the top of the bars, spreading out to the edges evenly. Top with the peanuts and toffee bits. Bake for an additional 20-25 minutes or until the center is set and topping is firm to the touch. Cool completely before cutting into bars.