Preheat your oven to 350°F (175°C) and prepare a 9×13-inch baking dish by giving it a good spritz with non-stick spray.

Whisk together the milk and chocolate pudding mix in a large mixing bowl until the mixture is smooth and slightly thickened.

Combine the chocolate cake mix with the pudding mixture directly, stirring gently until everything is just incorporated.

Fold in most of the chopped mini Reese’s Peanut Butter Cups, leaving a few to sprinkle on top later.

Pour the batter into your prepared baking dish, smoothing it out evenly. Sprinkle the reserved Reese’s on top to create that irresistible topping.

Bake for 25 minutes or until a toothpick inserted into the center comes out clean.

Cool the cake slightly before serving it warm or at room temperature.