Directions

1. Heat oven to 180C/160C fan/gas 4. Grease and line a 20 x 30cm rectangular cake tin with baking parchment - the best way to do this is with 2 long strips of parchment. Put the ingredients for the base in a food processor and blitz until it starts to clump together - don't worry if the peanuts are still a little chunky, they will add a lovely texture. Tip onto your work surface and knead briefly to bring together as a dough. Press the dough into the base of your tin in an even layer. Bake for 25 mins until golden, then set aside to cool.
2. To make the peanut butter layer, melt the butter and peanut butter in a small pan and mix until smooth. Sieve the icing sugar into a bowl, then pour in the hot butter mixture and stir to combine. While the mixture is still warm, pour over the base and smooth out with a spatula. Chill for 2 hrs until set.
3. To make the caramel layer, put the caramel and salt in a pan, bring up to the boil and simmer vigorously for 2-3 mins, whisking continuously, until the colour darkens a shade or two and the caramel thickens slightly. Leave the caramel to cool for 20 mins (see tips, below). Once cooled, pour it over the peanut butter layer and return to the fridge for a further 2 hrs.
4. Melt the chocolate in a heatproof bowl set over a pan of barely simmering water. Meanwhile, put the toffees and the milk in a small saucepan and gently heat. They will clump together and struggle to melt at first, but keep heating and eventually they will turn into a runny toffee sauce.
5. Remove the tin from the fridge and pour the chocolate over the salted caramel layer, tipping the tin to spread the chocolate over the surface. Use a spoon to quickly drizzle the caramel over the chocolate in a thin loopy pattern (or see tip, below). If the toffee starts to get too thick, add a splash more milk or cream and pop it back on the heat until runny. Sprinkle over the sea salt flakes and put the tin back in the fridge to chill for 2 hrs before slicing.