Step 1

Line base and sides of a 4cm-deep, 20 x 30cm (base measurement) slice pan with baking paper, extending paper 5cm over the long sides.

Step 2

Process biscuits in a food processor until finely crushed. Add butter and process until well combined. Transfer to prepared pan. Use a straight-sided glass to spread and press the mixture firmly over base. Place in the fridge for 30 minutes to chill.

Step 3

To make the fudge, place the white chocolate melts in a large heatproof bowl. Combine the coffee and boiling water in a small bowl until coffee is dissolved, then set aside.

Step 4

Melt the butter in a small saucepan over low heat. Add the condensed milk and cook, stirring constantly, for 2-3 minutes or until mixture is hot (be careful not to burn the mixture as it can easily catch on the base of the pan). Pour mixture over the white chocolate. Stir gently until chocolate melts. Stir in coffee and walnuts. Pour over biscuit base and spread evenly. Place in fridge for 2-3 hours or until firm.

Step 5

Meanwhile, to make caramel, heat cream and salt in a medium saucepan over medium heat until almost to the boil. Remove from heat. Meanwhile, stir the sugar, glucose and 185ml (3/4 cup) water in a saucepan over low heat for 5 minutes or until the sugar dissolves. Increase heat to high. Bring to the boil. Boil, without stirring, brushing down the side of the pan occasionally with a wet pastry brush, for 12-15 minutes or until golden. Remove caramel from the heat.

Step 6

Carefully stir the cream mixture into the caramel. Return mixture to medium heat, and cook, stirring constantly, for 3-4 minutes or until smooth. Set aside for 10 minutes to cool slightly. Add the butter and stir until melted and well combined. Pour over the fudge and set aside to cool at room temperature for 1 hour.

Step 7

Place dark chocolate and 1 tbsp oil in a small microwave-safe bowl. Microwave on HIGH, stirring every 30 seconds, for 1 minute 30 seconds or until smooth. Set aside.

Step 8

Place white chocolate and remaining oil in a small microwave-safe bowl. Microwave on HIGH, stirring halfway through, for 1 minute or until melted. Pour into a piping bag.

Step 9

Pour dark chocolate over caramel layer. Pipe thin lines of white chocolate over dark chocolate. Use a skewer to drag white chocolate through dark chocolate from top to bottom to create a feathered pattern.

Step 10

Place in the fridge for 4 hours to set. Remove from the pan and use a hot, sharp knife to cut into squares. Serve.