Heat the oven to 200C/180C fan/gas 6. Line the base of a 20cm square cake tin and lightly butter the sides. Blitz the flour, butter and sugar with a pinch of salt and 2 tbsp ice cold water in a food processor until you have a clumpy mixture. Press this into the prepared tin and bake for 25 mins until light golden. Set aside to cool completely.

For the caramel, place all of the ingredients in a saucepan. Melt everything together over a low-medium heat until the sugar has dissolved, then turn up the heat and bring to a gentle simmer. Stir continuously for 8-10 mins until the mixture has thickened and darkened a little. Pour the mixture over the biscuit base and chill for 2 hrs.

Once the caramel is set, melt the two chocolates in separate bowls, either in short bursts in the microwave or or set over a pan of gently simmering water. Spoon both chocolates over the caramel, then gently swirl it using a cocktail stick to create a marbled effect. Chill for a further 40 mins. Bring to room temperature before slicing into 12 squares.