1. 1. Preheat the oven to 350°F (175°C) and grease a 9x13 inch baking dish.

2. 2. In a large mixing bowl, combine the chocolate cake mix, melted semisweet chocolate chips, and pure vanilla extract. Mix well until smooth.

3. 3. Spread the chocolate mixture evenly into the prepared baking dish.

4. 4. In another mixing bowl, prepare the instant vanilla pudding mix according to package instructions.

5. 5. Dollop spoonfuls of peanut butter onto the chocolate mixture in the baking dish.

6. 6. Pour the prepared vanilla pudding over the peanut butter and chocolate layers.

7. 7. Use a knife to swirl the layers together for a marbled effect.

8. 8. Bake in the preheated oven for 25-30 minutes, or until set and slightly golden on top.

9. 9. Allow to cool before slicing into squares and serving.