- cooking spray
- 1 (16.5 ounce) package devil's food cake mix
- 1 cup water
- 1 cup peanut butter
- 1 cup chopped peanuts
- 3 eggs
- 1/3 cup vegetable oil
- 1 (14 ounce) can sweetened condensed milk
- 8 peanut butter cups (such as Reese's®), chopped
- 1 (8 ounce) container frozen whipped topping, thawed
- Preheat oven to 350 degrees F (175 degrees C). Grease a 9×13-inch baking pan with cooking spray.
- Combine cake mix, water, peanut butter, chopped peanuts, eggs, and vegetable oil in a large bowl; beat with an electric mixer on low speed until moistened, about 30 seconds. Beat at medium speed for 2 minutes. Pour batter into the prepared pan.
- Bake in the preheated oven until a toothpick inserted into the center comes out clean, 26 to 31 minutes. Poke holes in warm cake with a wooden skewer; pour sweetened condensed milk on top. Let cake cool, about 30 minutes.
- Sprinkle most of the chopped peanut butter cups over the cake. Spread whipped topping on top. Garnish with remaining chopped peanut butter cups.