Preheat oven to 220C/425F/Gas 7.
Place the flour and caster sugar into a bowl. Whisk in the egg and add just enough milk to form a batter, whisking until you have reached the consistency of double cream.
For the soufflé, place the egg yolks and sugar into a bowl and whisk togetherto combine.
Place the egg whites into a clean bowl and whisk until the mixture forms stiff peaks,when the whisk is removed.Carefully fold the egg white mixture into the whisked yolks.
Melt the butter in an ovenproof saucepan over a medium heat, and pour in a little of the crepe mixture, tilting the pan so the batter covers the base. Cook until the underside of the crepe is golden.
Place the chopped banana, nuts and chocolate onto half of the crepe and top with the soufflé mixture.
Fold the crepe in half with a spatula and transfer into the oven and cook for eight minutes, or until risen.
To serve, dust with icing sugar.
