Brush melted butter inside 2 dariole moulds. Refrigerate and brush with melted butter again. Dust with cocoa, turning the moulds to ensure the moulds are well coated.
Melt the chocolate and butter together in a heatproof bowl over a saucepan of simmering water. Stir gently to combine well into a dark silky liquid and set aside to cool a little.
Beat the egg, egg yolk and sugar together in a stand mixer fitter with a paddle attachment for at least 5 minutes, until the mixture is thick and moussey, and leaves a little trail before slowly sinking back into the rest of the mixture.
Carefully fold in the melted chocolate and butter. Sift the cocoa over the top and fold in carefully.
Divide the mixture between the prepared moulds and refrigerate for up to 6 hours before cooking.
Preheat the oven to 200 celsius (400 Fahrenheit) ( if using a fan forced oven set the temperature at 180 celsius (355 Fahrenheit)) and place a baking tray inside.
Place the fondants on top of the hot tray and bake 9–12 minutes. If the puddings will be sitting around for a few minutes before serving err on the side of caution and go for the shortest baking time. Leave for 1 minute before turning out into a bowl.
I've successfully made these puddings with coconut oil in place of butter. The flavour isn't quite as rich, but just as delicious, and a touch healthier.For an extra oozy and decadent pudding push a square of chocolate into the centre of the pudding before baking.