Preheat your oven to 180°C. Grease a 20cm square tin and line the base with baking paper.
Combine the oats, flour, coconut and cranberries in a bowl.
Place the butter, syrup and brown sugar in a small saucepan. Stir over a medium heat until the butter has melted and everything is combined. Stir in the bicarb.
Pour the melted butter mixture into the dry ingredients and mix well. Add the white chocolate chunks and mix. Scrape the mixture into your prepared tin and gently flatten into an even layer.
Bake the crunchies for 20 minutes, until they are golden and have risen slightly. They will still be a little wobbly in the middle. Leave to cool completely before cutting into squares.
Pop the remaining white chocolate in a small bowl and microwave on a low setting for a few seconds at a time whisking gently with a fork each time you check it. Once melted, pour the chocolate into a small sandwich bag. Snip off a corner of the bag and drizzle the chocolate over the cooled crunchies. (You could also use a small piping bag if you have one, or simply drizzle with a spoon.)
Allow the chocolate to set before serving. Store in an airtight container in a cool place.