Preheat your oven to 350°F (175°C) and grease a 9x13 inch baking dish.
In a large mixing bowl, combine the chocolate cake mix, melted butter, milk, eggs, vanilla extract, and salt. Stir until just combined; do not overmix.
Fold in the chocolate chips and chopped peanut butter cups until evenly distributed.
Pour the batter into the prepared baking dish and spread it out evenly.
Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted in the center comes out clean.
Allow the cake to cool for about 10 minutes before serving. Enjoy warm or at room temperature.