1. Coat the slow cooker with butter-flavor nonstick cooking spray.

2. In a medium-size bowl, whisk together the flour, cocoa, sugar, baking powder, and salt. Make a well in the center, add the milk, oil, and vanilla, and stir until well blended; continue stirring in widening circles, gradually incorporating the dry ingredients, until you have a smooth batter. Stir in the peanut butter (warm it in the microwave if thick and sticky from refrigeration); the batter will be thick. Stir in the chocolate chips. Spread evenly in the cooker.

3. To make the topping, in another medium-size bowl, combine the cocoa and sugar; pour in the boiling water and whisk until smooth. Gently pour over the batter in the cooker; do not stir. Cover and cook on HIGH until puffed and the top layer is set, 2 to 2¼ hours.

4. Turn off the cooker and let stand, covered, for at least 30 minutes before serving.

5. To serve, scoop the cake into individual bowls. Add a scoop of vanilla ice cream alongside the cake. Spoon some of the fudgy pudding over the cake and ice cream and serve.