PREPARE: Heat the oven to 180°C / 350°F / Gas 4. Butter a 18cm x 28cm (7 x 11 in.) baking dish, then line it with baking parchment paper - it helps to cut triangles out of the corners of the baking paper so that it fits flush in the dish.

SHORTBREAD LAYER: In a large bowl, whisk together the flour, sugar, and salt, then add the butter. The butter should be very soft, so you should be able to easily squeeze it together with your thumb and forefinger. Mix the ingredients together with a wooden spoon or your hands until they look like rough crumbs. Add the egg yolk and knead until you have a crumbly dough.

BAKE SHORTBREAD: Tip the shortbread mixture into the prepared pan and press it firmly and evenly across the base. Prick all over with a fork, then bake in the preheated oven for 15-20 minutes until golden and browning around the edge. Set aside to cool for at least 15 minutes before you begin the caramel, leaving the oven on.

CARAMEL LAYER: Add all caramel ingredients to a heavy-bottomed saucepan. Cook over medium-low heat, stirring for 5-7 minutes until the mixture thickens and begins to smell and look like delicious caramel. Watch out for spitting sugar!

BAKE CARAMEL: Remove the saucepan from the heat, then pour caramel over the shortbread base. Give the baking dish a little shake to even it out, then bake in the oven for 15 minutes. The caramel will bubble and turn golden brown, it may even have a few scorched spots, but that is fine; you’ll cover it with the chocolate later. Cover it loosely with foil if it looks like it is about to burn (it shouldn’t). When cooked, remove from the oven and cool for 15 minutes.

SERVE: To serve, remove from the fridge, allow to warm slightly for 5 minutes, then use a long, sharp knife to cut into pieces, dipping the blade in water and wiping clean between each cut. Sprinkle with sea salt flakes before serving.