Prepare for baking: Preheat your oven to 180 °C (350 °F) standard (or 160 °C / 320 °F fan‑forced). Grease and line an 8‑inch (20 cm) square baking pan with parchment or baking paper, ensuring two sides overhang so you can lift out the bars later.

Make the brownie layer: In a large mixing bowl, add the melted butter, sugar and vanilla. Whisk gently to combine. Then add the two eggs one at a time, followed by the egg yolk, mixing until smooth. Next add the sifted cocoa powder, flour and salt. Stir just until combined—avoid over‑mixing.

Bake the brownie base: Pour the brownie batter into the prepared pan, spreading it evenly. Bake for approximately 25 – 30 minutes, or until the edges are set and the centre looks slightly fudgy. Remove from oven and allow to cool completely. If you’re prepping ahead, you can cover and place it in the fridge.

Prepare the peanut butter layer: Once the brownie base is fully cooled, take a large mixing bowl and add the softened butter and peanut butter. Use an electric mixer on medium speed and whip until creamy. Then add the icing sugar and mix until smooth and well‑combined. Spread this peanut butter filling evenly over the cooled brownie layer and smooth the top. Place the pan back into the fridge to chill.

Make the chocolate crunch topping: Heat the dark chocolate pieces in the microwave, stirring every 20 seconds until melted and smooth. Quickly stir in the Rice Bubbles (or Rice Krispies) until the cereal is completely coated by the chocolate. If you like, add a teaspoon of vegetable oil or coconut oil to help the chocolate top slice more cleanly later.

Assemble and chill: Pour the chocolate cereal mixture over the peanut butter layer and spread as evenly as possible. Place the entire pan in the fridge (or freezer if you’re short on time) for at least 2 hours, or until the layers are firm.

Slice and serve: Using a hot knife (run under hot water and wipe dry) carefully cut into small slices. Serve chilled or at room temperature, as you prefer.