Preheat the oven to 180C/160C fan/gas mark 4. Grease and line with baking parchment 3 x 20cm sandwich tins.

For the cakes, put the butter, sunflower oil and chocolate into a heatproof bowl and place this over a pan of barely simmering water. Allow the chocolate and butter to melt into the oil – this might look split and curdled when hot, but that’s absolutely fine. Remove from the heat and set aside to cool slightly.

Sift the dry ingredients into a bowl. Now whisk in the buttermilk and eggs into the cooled melted chocolate mix. Add the wet ingredients to the dry ingredients (use a freestanding electric mixer fitted with whisk attachment for ease) and whisk together until completely smooth. Divide the batter evenly between the prepared tins and bake for 20-25 minutes, until a skewer inserted into each cake comes out clean. Allow the cakes to cool completely, in their tins. Once the cakes are cool, remove from the tins and cut them in half with a long serrated knife to create 6 layers.

For the curd, place the lime juice, butter and zest into a medium saucepan and heat over medium/high.

Meanwhile whisk together the yolks and caster sugar - adding a tablespoon of lime juice if it’s a little thick - then whisk in the cornflour. Once the butter has melted bring to the boil, pour half onto the eggs and sugar, whisking constantly to blend, then pour that back into the pan and heat again, whisking constantly until the mixture is extremely thick.

Empty the curd onto a plate, cover with cling film end ensure the film touches the surface of the curd to prevent a skin forming, and refrigerate until cold.

Roughly chop the chocolate and put it into a heatproof bowl. Put the cream into a saucepan and heat until it starts to simmer. Pour the hot cream over the chocolate, wait for 30 seconds, then whisk until the ganache is glossy. If there are any lumps of chocolate in the ganache, set the bowl over a pan of barely simmering water and allow it to melt until smooth. Pour the ganache onto a sided baking tray and allow it to cool until it is thick but spreadable.

Spread a dollop of ganache onto a cake stand, plate or cake card to hold the cake in place then place one layer of cake and spread a third of the ganache on top. For ease use a small, crank-handled palette knife and turntable for this part, and it’s important to keep it clean in between layers. Place another layer of cake on top, then spread over scoop of the lime curd - though don’t use too much, as it will make the cakes slip and slide around. Repeat until you have 6 layers of cake, 3 layers of ganache and 2 layers of lime curd. Chill the cake for at least 30 minutes in the fridge.

For the meringue frosting, put the egg whites, sugar and golden syrup into a heatproof bowl and set over a pan of barely simmering water. Using a handheld electric whisk, whisk the meringue for at least 5 minutes on the heat, then remove the bowl from the heat and whisk for a further 5 minutes until you have a very thick meringue. Spread enough of the meringue over the top and sides of the cake to cover it completely, then using a dough scraper or palette knife, scrape off the meringue around the sides of the cake to reveal patches of chocolate cake underneath to create a semi-naked finish.

Put the remaining meringue into the piping bag fitted with the 14mm plain nozzle, and put the remaining ganache into a piping bag fitted with the other 14mm nozzle. Pipe alternate teardrop blobs of meringue and ganache over the top of the cake – do a ring of blobs on the outside edge, then repeat in circles to the centre. Finish the cake by coarsely grating over a little more chocolate.