Put the caster sugar in a medium sized heavy saucepan over a medium heat. After a few minutes the sugar will start. At this point you can shake the pan but do not stir it. After a few more minutes the sugar will have melted completely and turned a rich golden brown.
Take the saucepan off the heat and add the butter and stir in completely before adding the double cream.
Return the salted caramel sauce to the heat and stir constantly. After a minute or two it will turn to a liquid syrup which is totally smooth. Remove the pan from the heat.
When it has cooled a little check the flavour and add a few flakes of sea salt until you have the desired taste. Leave to cool.
Salted Caramel Crème Diplomat
Put a tablespoon of sugar in a bowl with the gg yolks and whisk together until well combined. Whisk in the cornflour and set aside.
Measure out the butter, cut into cubes and place it in the fridge until the next step.
In a saucepan put the remaining sugar, milk and 60ml of double cream. Bring to a simmer and stir once or twice to make sure that the sugar melts. When the milk mixture comes to a simmer take it off the heat and slowly add it to the egg yolks, whisking all the time.
Return the mixture to the saucepan and heat whilst stirring until the mixture thickens then remove from the heat and whisk in the butter from the fridge.
Cover with clingfilm and chill in the fridge.
Whip the cream until stiff. Stir in 60ml of the caramel sauce amd the vanilla essence. Fold in the cream, recover and refrigerate for an hour.
Pastry
Use pastry lready rolled into a rectangle. It should be about half a centimetre thick. Cut the pastry into 3 equal pieces length ways. Heat the oven to 200 C and place the pastry on baking sheets lined with baking parchment. Place another piece of baking parchment on top and cover with another baking sheet. Bake for about 10 minutes then remove the top baking sheet and paper and return to the oven until golden brown and cooked.
Cool on a wire rack and then cut each piece into 6 even pieces. You may need to trim the pastry all the way around the outside edge to start with too.
Salted Caramel Icing
Mix the icing sugar and mix into the remaining caramel sauce. You may need to warm it so that you can easily stir it in.
Assembly
Use a piping bag with a large plain nozzle to divide the mixture evenly between 6 pieces of pastry then spread out over the pastry completely with a knife.
Put the crème diplomat in another icing bag with a medium star nozzle and pipe rosettes, (about 14 in total), along 6 base pieces of pastry. Top each with another piece of pastry and pipe another layer. Top with the iced layer.