Chocolate Peanut Butter Cake for a Crowd

Step 1: Preheat the oven to 180°C/350°F (160°C fan).

Step 2: Grease a 23 x 33 cm (9 x 13-inch) metal cake pan with butter. Line it with paper, leaving an overhang to make the cake easier to lift out.

Step 3: Sift the flour, cocoa, baking powder, and baking soda into a large bowl. Add the sugar and salt, then whisk briefly to combine.

Step 4: Add the eggs, milk, oil, and vanilla. Whisk until lump-free, about 30 seconds.

Step 5: Add the coffee powder, if using, then pour in the boiling water. Whisk to combine. The batter will be very thin. Pour it into the prepared pan.

Step 6: Bake for 45 minutes, or until a wooden skewer inserted into the center comes out clean.

Step 7: Cool for 10 minutes, then cool completely on a wire rack before frosting, about 2 hours.

Step 8: Beat the butter on high for 3 minutes, using a stand mixer with the paddle attachment or a handheld beater, until soft and fluffy.

Step 9: Add the icing sugar in 3 batches. Start beating on low speed, then increase the speed to incorporate each batch without scattering the sugar. Add the next batch once the previous one is incorporated.

Step 10: Once all the icing sugar is incorporated, add the peanut butter, salt, and milk. Beat on high for 3 minutes, until fluffy.

Step 11: Put the chocolate and cream in a small bowl. Microwave on high in 15-second bursts, stirring between each, until smooth. Cool for 10 minutes before using.

Step 12: Spread all the frosting over the cake, right to the edges.

Step 13: Drizzle half the chocolate mixture and the melted peanut butter over the cake. Scatter the peanut butter cups on top. Drizzle with the remaining chocolate and peanut butter, then sprinkle with the chopped peanuts.

Step 14: Cut the cake into pieces and serve immediately. Refrigerate leftovers for up to 5 days. Bring them to room temperature before serving, as the frosting firms up when cold.