Line a 20cm × 30cm slice tin with baking paper, allowing the paper to overhang slightly on two sides.

In a medium saucepan over low heat, melt the butter, caster sugar and honey together, stirring gently until smooth, about 3 minutes.

Crush the Weet-Bix by hand into bite-sized pieces (not fine crumbs) and add to the pan with the desiccated coconut.

Stir until well combined and the mixture is evenly coated, about 1 minute.

Press the mixture firmly and evenly into the prepared tin using the back of a spoon or bench scraper.

Set aside while you make the icing.

In a medium saucepan over low heat, melt the butter until foaming, about 2 minutes.

Remove from heat and add the cocoa powder, stirring until smooth with no lumps, about 1 minute.

Add the sifted icing sugar and vanilla extract, stirring to combine.

Gradually pour in the milk, a little at a time, stirring until you reach a spreadable consistency—the icing should be thick but pourable.

Immediately spread the warm icing over the base in an even layer using a spatula or back of a spoon.

Allow to cool at room temperature for 20–30 minutes until the icing is just set but still slightly tacky.

Once cooled, refrigerate for at least 30 minutes until the icing is completely firm.

Using the overhanging baking paper, lift the slice out of the tin onto a chopping board.

Using a sharp knife dipped in hot water and wiped clean between cuts, cut into 16 even squares.

Store in an airtight container at room temperature.