Preheat oven to 180 degrees Celsius (160 degrees Celsius fan-forced). Lightly grease and line with baking paper an 18cm by 28cm slice pan.

In a small saucepan, melt chocolate and butter together over very low heat, stirring frequently. When it's just melted, remove from heat and stir in the golden syrup.

Using your fingers, crush the Weetbix by breaking them up to a fairly fine consistency.

Stir together the coconut, brown sugar, weetbix and both flours together in a large bowl until well combined. Add in the chocolate mixture, stir to combine. Firmly press mixture into prepared pan using the back of a spoon or with a round glass. Take care to press it evenly into the pan, particularly into the corners. Bake slice for 15 minutes.

Make chocolate icing while slice is baking. Sift icing sugar and cocoa together into a medium bowl. Add butter and milk and stir until smooth. The icing should be quite thick at this stage; however, it will spread easily when placed on the hot slice.

Remove slice from oven and set aside for one minute before spreading the icing. Sprinkle the coconut on top.

Allow slice to cool to room temperature before cutting into pieces to serve. Store slice in an airtight container in the pantry for up to 1 week. Alternatively, freeze it for up to 3 months.