Line your square pan with parchment paper, leaving overhang on the sides for easy removal.
In a microwave-safe bowl, melt the butter at 30-second bursts, stirring in between until completely smooth and bubbling slightly.
Add the cocoa powder to the melted butter and stir well until the mixture turns glossy and deep brown, releasing a rich, chocolatey aroma.
Pour in the honey or maple syrup, stirring thoroughly to combine into a smooth, shiny chocolate mixture.
Gently fold in the crispy rice cereal with a spatula, making sure each piece is coated in the chocolate mixture. You should hear a soft crackle as the cereal hits the wet chocolate.
Transfer the mixture into the prepared pan and press it firmly into an even layer using the back of your spatula. This helps the bars set up tightly and keeps them crunchy.
Cover the pan with parchment or plastic wrap and place it in the fridge for at least 2 hours, or until the mixture is set and firm to the touch.
Once chilled and firm, lift the block out of the pan using the parchment overhang and place it on a cutting board.
Use a sharp knife to cut the mixture into bars or squares, wiping the knife clean between cuts for neat edges.
Arrange the bars on a plate or store in an airtight container at room temperature for up to 3 days, or refrigerate for longer freshness.
