Cake – Line a 6-quart oval slow cooker with a slow cooker liner or spray with cooking spray; set aside.
To a large bowl, add the cake mix, water, eggs, peanut butter, butter, and beat with an electric handheld mixer on medium-high speed for about 2 minutes; stop to scrape down the sides of the bowl as necessary. The batter will be thick.
Turn just over half of the batter out into prepared slow cooker.
Add the hot fudge and top with the remaining batter.
Using a knife or rubber spatula, lightly swirl up and back the length of the slow cooker.
Cook on high for about 1 hour 45 minutes, or until a knife inserted in the center comes out clean, or with a few moist crumbs. Because all slow cookers vary, start checking at 1 hour 30 minutes. When cake is done, remove the ceramic base from slow cooker and place the base on a wire rack to cool. While cake cools, make the glaze.
Glaze and Toppings – To a medium bowl, add the confectioners’ sugar, peanut butter, milk, and whisk until smooth. Add additional milk as necessary until desired glazed consistency is achieved. Turn glaze out evenly over the cake.
Evenly drizzle the hot fudge over over the glaze and lightly swirl it into the glaze.
Evenly sprinkle the peanut butter cups and serve immediately. Cake is best fresh but will keep airtight for up to 5 days.
enjoy!
