Preheat oven to 180°C fan bake. Line a slice tin with baking paper.
In a large saucepan over low heat, melt together the butter, sugar and cocoa.
Remove from the heat and stir in crushed Weetbix, flour, coconut and baking powder until well combined.
Pour mixture into the prepared tin and press down firmly.
Bake for 15–20 minutes until just cooked – the centre should still feel soft to the touch.
While still hot, place the block of chocolate over the slice. Turn off the oven and place the slice back in for 3–5 minutes until the chocolate has melted.
Remove from the oven and use a spatula to spread the melted chocolate to the edges.
Chill in the fridge or freezer until set, (if you can wait that long) then slice into pieces and serve.
