- Preheat the oven to 180°C / fan 160°C / gas mark 4. Grease a 20cm square tin and line with the provided baking paper. In a large bowl, briefly beat 110g of butter until soft, then gradually add bag 1. Mix until a soft dough forms.
- Put the shortbread dough into the prepared tin and press into the base using your fingers. Smooth over the dough with the back of a spoon for an even layer.
- Bake the shortbread for 15-20 minutes, or until lightly golden around the edges. Remove from the oven and leave to cool in the tin on a wire rack. Whilst still slightly warm, if the shortbread has come away from the sides, gently use the back of a spoon to push it back to the edges. Leave to cool completely.
- When the shortbread has cooled, begin to make the caramel. In a medium saucepan over a low heat, melt together 150g of butter with bag 2. When the butter has melted and the sugar has dissolved, add the tin of Carnation Condensed Milk and mix to combine. Increase the heat slightly and bring the caramel to a boil, stirring continuously.
- cook for a further 4-5 minutes, stirring constantly to avoid it catching on the bottom of the pan, until the caramel has thickened slightly. Pour the caramel onto the cooled shortbread base and leave to one side to cool for 20 minutes, then chill in the fridge for 1 hour until firm enough to top with the chocolate.
- Once the caramel is set, begin to make the chocolate layer. Over a low heat, stir together 35g of butter and bag 3 in a saucepan, until melted. Pour the chocolate topping over the set caramel and spread to the edges to create a smooth, thin layer of chocolate.
- Empty bag 4 into a heatproof bowl. Melt in the microwave in 10 second intervals, stirring after each interval until melted. Alternatively put the bowl over a pan of simmering water, ensuring the bowl doesn’t touch the water, and mix until smooth and melted. Transfer to the provided piping bag and snip a small corner off of the bag. Pipe lines vertically on top of the dark chocolate, about 1cm apart, then drag a knife or skewer horizontally through a white chocolate in alternating directions to give a feathered effect.
- Chill in the fridge for 1-2 hours, or until the chocolate topping has completely set. Remove from the fridge and rest for 5 minutes. Remove from the tin and cut into 16 squares. For a clean cut, run a sharp knife under hot water, and wipe clean before cutting each slice.