Heat oven to 160C/140C fan/gas 3.
Grease and line a 25cm round deep cake
tin with baking parchment. In a large
bowl, mix the oil, egg yolks, vanilla paste,
caster sugar and 200ml water until well
combined. Sift in the cocoa powder and
whisk until smooth.
Sift in the flour, bicarb and 1 tsp salt.
In a separate bowl, whisk the egg whites
to stiff peaks. Fold into the batter with
a large metal spoon and mix until
everything is well combined.
Gently pour the mixture into your cake
tin, then bang it on the work surface twice
to expel any large air pockets. Bake for
1 hr 10 mins or until the cake springs back
when gently prodded and an inserted
skewer comes out clean. (Cover with foil
after 1 hr if the cake starts to get too
dark.) Remove from the oven, cool in the
tin for 10 mins, then transfer to a large
wire rack and peel off the parchment.
Leave until the cake is completely cool.
Make the salted caramel icing while
the cake bakes. Heat the brown sugar,
½ tsp salt and cream in a saucepan
until the sugar has dissolved. Bubble
for a few mins, then leave to cool
completely. Beat the butter until smooth,
pour in the cooled cream mixture and
continue mixing until softly whipped.
Chill until needed.
To make the ganache, heat the cream
until just boiling. Remove from the heat
and pour over the chocolate. Leave to
stand for a few mins until the chocolate
has melted and you have a smooth sauce
consistency. Leave to cool at room
temperature until the ganache is a
pipeable thickness, then transfer to a
piping bag fitted with a star nozzle. To
finish the cake, slice in half and fill with
the salted caramel buttercream. Pipe tall
spikes of chocolate ganache on top and
decorate with the sea salt crystals. Will
keep for up to 2 days in a cool place.