Ingredients
Cake
225g (scant 2 cups) plain flour350g (1 + 3/4 cups) caster (superfine) sugar
85g (2/3 cup + 1 tsp) cocoa powder
1 1/2 tsp baking powder
1 1/2 tsp bicarbonate of soda (baking soda)
2 eggs
250ml (1 cup + 2tsp) buttermilk
125ml (1/2 cup + 1tsp)vegetable or sunflower oil
2 tsp vanilla extract
250ml (1 cup + 2tsp) very hot coffee or boiling water
Salted Caramel
300g (1 1/2 cups) caster (superfine) sugar
60ml (1/4 cup) water
280ml (1 cup + 3tbsp) double cream
30g (2 tbsp) unsalted butter
1/2 tsp - 1 tbsp sea salt flakes
Swiss Meringue Buttercream
200g (1 cup) caster (superfine) sugar4 large egg whites
250g (1 cup + 1 tbsp) softened unsalted butter
1 tsp vanilla extract
6 tbsp (or more to taste) salted caramel
Whipped Ganache
200g (7 oz) dark chocolate200ml (3/4 cup + 1tbsp + 1tsp) double cream
Preparation
1.Bake the cake the day before you want to ice it. Preheat the oven to 180°C/350°F/Gas mark 4. Grease and line two 20cm/8in round tins.
2.Sift the flour, cocoa powder, baking powder and bicarb of soda together into a large bowl, stir in the sugar. In a separate bowl, whisk together the eggs, buttermilk, oil and vanilla extract, pour into the dry ingredients and beat well until smooth and combined. Add the hot coffee, a little at a time, until it is all combined, the mixture will be very liquid, don't panic! Divide the batter between the tins and place in the centre of the oven, check after 35 minutes - a skewer inserted into the centre should come out clean or with a few moist crumbs, but no wet batter. They could take up to an hour to bake though, mine took 55 minutes, just check every 5-10 minutes after the 35 minute mark.
3.Once baked, remove to a wire rack, still in their tins, and leave to cool completely. Once cold, wrap the cakes in their tins in clingfilm and place in the fridge overnight, or for at least an hour. It is far easier to slice a cold cake in half neatly.
4.Make the salted caramel: Place the sugar and water into a deep, heavy-bottomed saucepan, bring to the boil and cook, swirling the pan, NOT stirring, until the sugar dissolves and the colour changes to amber. Remove from the heat and pour the cream - be careful as the caramel will bubble ferociously and rise up in the pan. When the bubbling stops, add the butter and whisk till combined, it may not be completely smooth at this point.
5.Return the pan to a medium heat and cook at a gentle simmer, whisking the whole time, for a couple of minutes until the caramel is smooth and free of lumps. Whisk in the salt, a little at a time, tasting as you go (CAREFULLY - the caramel is very hot!), until it's at the right level of saltiness for you. Make sure that the salt is actually fully combined, and not just sinking to the bottom, before adding more. Leave the caramel to cool completely, it can be made the day beforehand and stored in the fridge for up to a week.
6.To make the salted caramel swiss meringue buttercream, put the egg whites and sugar in an extremely clean heatproof bowl (use the bowl of your stand mixer if you have one). Place over a pan of simmering (not boiling) water (do not let the base of the bowl touch the water) and whisk with a hand whisk (not electric) until the sugar has dissolved completely and the mixture is warm to the touch, if you rub some of the mixture between your fingers it should be smooth and you shouldn’t be able to feel any graininess, this will take about five minutes. If you want to get technical about it the mix should reach 60°C/140°F on a thermometer.
7.Remove the bowl from the heat and attach it to your stand mixer with the whisk attachment or use an electric hand whisk, whisk the egg whites until it forms a thick, glossy, bright white meringue and is completely cool, the bottom of the bowl should feel cool to the touch, this will take about 10 minutes.
8.Once the meringue is cold, switch the mixer to a low speed and begin to add the butter, a tablespoon at a time, make sure that each addition is fully incorporated before adding the next; the meringue will deflate a little and may begin to look curdled, don’t panic! This is normal, just keep adding the butter gradually and whipping away and it will come back together. If, once all the butter has been added, your mixture is runny, the butter may have been too soft or the meringue still warm, just put the bowl in the fridge for 15 minutes or so then carry on whipping.
9.If, even after a decent amount of whipping, it still looks curdled, place about 4 tablespoons worth of the mixture in a small bowl and microwave for 10-15 seconds, it should become runny, pour this back into the bowl of buttercream, down the side of the bowl while whisking, continue to whisk for a few minutes and it should come back together. Once the buttercream is completely smooth and silky and all the butter has been incorporated, whisk in the vanilla extract and salted caramel.
10.Remove the cakes from the fridge and carefully, using a long, sharp serrated knife (like a bread knife) slice each one in half so you have four layers. Place one layer on a serving plate or cake stand and spread over just over a quarter of the buttercream, then drizzle over a tablespoon or two of the salted caramel (you can thin it with a little more cream or warm it VERY slightly until it becomes pourable if needed - I'm talking no more than 10 seconds in the microwave, do not let it become warm or it will melt the buttercream). Top with another layer of cake and repeat until you have three layers of buttercream; place the final layer of cake on top - use one of the bottom halves, upside-down, so that you have a flat top.
11.Spread the remaining scant quarter of buttercream thinly all over the cake, it does not need to be neat and you will be able to see cake through the buttercream but try to get it fairly smooth and cover the cake evenly; this is your crumb coat - it will stop cake crumbs from getting into your ganache. Place the cake in the fridge for at least fifteen minutes while you make the ganache.
12.To make the ganache, chop the chocolate and place in a heatproof bowl. Put the cream in a small pan and heat until just simmering, pour it over the chocolate, making sure that it is all covered; leave to stand for 5-10 minutes then stir until smooth. Leave the ganache until it has cooled to room temperature - it should have thickened but still be spoonable, like pudding (you can pop it in the fridge to speed this up). Whisk with an electric whisk until it has lightened in colour and has the texture of thick whipped cream, do not overwhip or you will end up with chocolate butter...which sounds delicious but is not what we want here! Immediately spread the ganache all over the cake - work fairly quickly as it doesn't take long for it to start to set.
13.To finish, drizzle over the remaining salted caramel.