Preheat a flat baking sheet in the oven set to 200C/400F/Gas 6.
To make the fondant, whisk the egg white until stiff then fold in the flour and cornflour.
In a separate bowl mix together the melted chocolate, sugar and egg yolk.
Mix one spoonful of the whisked egg white into the chocolate, then add the rest of the white and fold together.
Butter two dariole moulds and dust with cocoa powder.
Spoon the mixture into the moulds, then bake in the oven for 10 minutes.
To make the chocolate sauce, in a bowl mix the water and caster sugar with the melted chocolate.
To serve, turn the fondants out onto a plate, garnish with the ice cream and spoon around some of the chocolate sauce.
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