In a large mixing bowl, combine the instant pudding mix with 2 cups of milk. Whisk vigorously for about 2 minutes until the mixture is smooth and slightly thickened.

Sift in the chocolate cake mix and gently fold into the pudding mixture using a spatula for approximately 1-2 minutes.

Roughly chop the peanut butter cups and fold them into the batter until evenly distributed.

Pour the batter into a greased 13 x 9-inch baking dish and bake at 350°F (180°C) for about 25 minutes.

Remove from the oven and allow to cool for about 10 minutes before serving.