Preheat the oven and Prepare the Pan - Preheat the oven to 350 degrees Fahrenheit and grease the pan.
Prepare the Cake Mix - In a large bowl, combine cake mix, peanut butter, canola oil, and egg. Mix until the ingredients are fully combined.
Bake the Mix - Add two-thirds of the peanut butter mix to the pan. Bake for ten minutes and allow to cool for five minutes on a wire rack.
Prepare the Fudge - On low heat, combine the sweetened condensed milk, semi-sweet chocolate chips, and butter in a heavy saucepan. Stir until smooth, then pour over the peanut butter mixture and sprinkle with the remaining peanut butter mixture. Be careful while pouring the fudge, as it will be hot.
Bake the Mix - Bake for 20-25 minutes, until golden brown. Allow to cool on a wire rack and then cut into bars.
These peanut butter bars are great treats for bake sales, games, parties and any sort of occasion. Both kids and adults will love the perfect combination of chocolate and peanut butter.