Heat the oven to 180C/160C fan/gas 4. Butter and line three 20cm cake tins. Put all the dry ingredients into a stand mixer along with ½ tsp of salt and mix on a low speed with a balloon whisk. In a large jug or bowl, whisk together the eggs, buttermilk and oil. Slowly pour the wet ingredients into the mixer, while gradually increasing the speed to medium. Turn the speed to low again and gradually add 450ml of freshly boiled water. Whisk until just incorporated, being careful not to overmix. Divide the batter across the three tins and bake for 40-45 mins, using a toothpick to check they are cooked through.

While the sponges bake, make the syrup by combining 150ml of water and the sugar in a small pan. Cook over a low heat for 5-6 mins or until the sugar has dissolved. As soon as the sponges are cooked, douse with half of the warm syrup. After 20 mins, run a small paring knife along the edges of the cake tins and turn out the sponges. Soak the other sides with the remaining syrup. Leave the cakes to cool.

While the sponges are cooling, make the ganache. Put a bowl over a pan of simmering water and add the chocolates, allowing them to melt. Gently warm the cream in a small pan, then pour over the melted chocolate, allowing to sit for a minute. Blend with an immersion blender, making sure the head does not reach the surface so as not to create air bubbles. Alternatively, you can whisk the ganache by hand. Add the butter bit by bit and continue blending until the ganache is emulsified and shiny. Put clingfilm directly on the surface of the ganache. Allow to cool and set fully at room temperature.

Finally, make the buttercream. In a bowl, whisk together the egg whites, sugar, cream of tartar and a pinch of salt, then put the bowl over a pan of simmering water. Use a sugar thermometer to check when the mixture gets to 71C, then transfer the mixture to a stand mixer bowl and whisk the meringue to stiff peaks and until the bowl is no longer warm to touch.

Change the attachment to a paddle beater and mix on a medium speed. Gradually add the butter and mix on a high speed until the buttercream is smooth and silky. The mixture will look curdled at first but keep on mixing as it will all come together. Scrape the seeds out of the vanilla pod and add to the buttercream along with the melted chocolate. Beat until thick and glossy.

To assemble, sandwich then crumb coat the cake with the ganache. Chill in the fridge or freezer for 20 mins. Cover the cake with the buttercream, smooth out the edges and swirl the top with a palette knife. Chill again for 20 mins. To create the wooden pattern, pipe the sides using a 1M large star piping nozzle, piping from the bottom to the top in a wavy line. Pipe rosettes in random areas, to make it look like a rustic woodland. Decorate with sprigs of rosemary, broken cinnamon sticks, dark chocolate bark and gold lustre spray.