- Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking dish. 
- In a large mixing bowl, combine the chocolate cake mix, milk, melted butter, and vanilla extract. Stir until just combined; do not overmix. 
- Pour the batter into the prepared baking dish, spreading it evenly. 
- Drop spoonfuls of peanut butter over the cake batter. Use a knife or skewer to swirl the peanut butter into the batter gently. 
- Sprinkle the chocolate chips and chopped peanut butter cups evenly over the top of the batter. 
- 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. Dust with powdered sugar if desired.