Line an 8-inch square baking pan with parchment paper.

Place the crushed biscuits and shredded coconut into a large mixing bowl.

In a saucepan over low heat, melt the butter with brown sugar, cocoa powder, and condensed milk until smooth and glossy.

Stir in the vanilla extract and remove from heat.

Pour the chocolate mixture over the biscuit mixture and fold together until evenly coated.

Add the milk chocolate chunks and gently mix through.

Transfer the mixture into the prepared pan and press firmly into an even layer.

Melt the dark chocolate with heavy cream in a microwave-safe bowl in 20-second intervals, stirring until smooth.

Spread the melted chocolate evenly over the slice mixture and lightly tap the pan to smooth the surface.

Sprinkle with extra coconut flakes if desired.

Refrigerate for at least 3 hours or until firm.

Slice into rustic squares and serve chilled or slightly softened at room temperature.