Begin by greasing a 20 x 20 cm baking tin with a little butter and lining it with parchment paper.

Using a food processor or a rolling pin, crush the Arnott's Marie biscuits into fine crumbs.

In a medium bowl, combine the instant coffee granules, cocoa powder, and light brown sugar. Pour in the boiling water and stir until smooth.

In a large mixing bowl, combine the crushed biscuits, sweetened condensed milk, desiccated coconut, melted butter, and vanilla extract. Add the coffee mixture and mix well.

Transfer the mixture into the prepared tin and press it down firmly to create an even layer.

In a microwave-safe bowl, combine the milk chocolate and additional salted butter. Microwave in intervals, stirring until smooth.

Pour the icing over the cooled base and spread it evenly.

Place the tin in the refrigerator for at least 2 hours to set completely.