Preheat the oven to 200C/400F/Gas 6 and place a baking tray in the oven to heat.
In a large bowl whisk the egg whites until stiff peaks form. Gradually add the sugar and continue whisking until light and fluffy. Stop when the mixture is thick enough to leave a ribbon-like trail when the whisk is lifted.
Heat the milk in a small saucepan to scalding point. Add the 25g/1oz butter and allow it to melt, then add the cornflour, ground ginger and vanilla extract. Whisk until thick. Pour into a large bowl and mix in the lime zest.
Spoon a little of the egg white mixture into the lime and ginger mixture and mix well. Carefully fold in the rest of the egg white mixture, making sure to maintain the volume.
Fill two greased ramekins with the mixture and place on the hot baking sheet and into the oven. Cook for 10 minutes until the soufflés have risen.
To serve, place the soufflés on the centre of a plate and dust with icing sugar.