For the saltedcaramel sauce
— 100g caster sugar — 30g unsalted butter — 175ml single cream — generous sprinkle of sea-salt flakes Preheat the oven to 180C/160C fan/gas mark 4. Dot a 26-28cm springform cake tin with butter and line with parchment paper.
Place the broken chocolate and caster sugar in a food processor, and blitz until it turns to fine crumbs. Add the egg yolks, butter, vanilla extract and 175ml boiling water. Blitz again until thoroughly combined.
In a large bowl, whisk the egg whites until they form stiff peaks. Set to one side.
Pour the chocolate mixture into a separate large bowl and gently fold in the whisked egg whites. Once combined, pour the mixture into the lined cake tin, dot in the peanut butter and swirl using a knife.
Bake for 45–50 minutes. It’s quite a moist cake but should no longer have a wobble to it. It will sink a bit when you take it out of the oven, and is likely to crack a little too.
For the salted-caramel sauce, add the sugar to a large frying pan and place over a medium heat. Once the sugar has melted, add the butter, stirring the whole time, then add the cream. Once this has turned to caramel, add the salt.
Serve the cake warm or cool with the warm sauce. It will also keep really well in the fridge, so you can make it a day or two in advance of a dinner party.