Line a slice tray 30 cm x 20 cm with baking paper.
In a large glass bowl, heat the butter in the microwave for 40 seconds until melted. Stir in the condensed milk.
Place the biscuits in a food processor, one packet at a time. Add the desiccated coconut with the first packet and blitz until fine crumbs form. For the second packet, blitz but leave larger chunks.
Combine the crushed biscuits and coconut with the butter and condensed milk mixture in the bowl. Add the lemon zest and juice and mix until well combined.
Press into the lined baking tray, flattening it down evenly and spreading out to the edges. Place in the fridge while you prepare the icing.
Add the icing ingredients to a bowl then whisk together until smooth. Spread the icing evenly over the base.
Place the tray in the fridge and let it set for 3+ hours or overnight.
Once set, cut into pieces and store in an airtight container in the fridge for up to a week.
