1 Preheat the oven to 190°C(170° fan)|375F|gas 5. Grease four heatproof tea cups with a little softened butter. Chill until ready to use.
2 Melt the remaining butter in a saucepan set over a medium heat. Whisk in the flour and cook for 1 minute, whisking, until thickened.
3 Whisk in the milk and cook until thickened, 2 minutes. Stir in the chocolate and two tablespoons of the sugar. Remove the saucepan from the heat and beat in the egg yolks.
4 Beat the egg whites with a pinch of salt until stiffly peaked. Add the remaining caster sugar and beat until thick and glossy.
5 Stir one third of the beaten egg white into the chocolate mixture. Fold in the rest using a rubber spatula and divide the batter between the buttered tea cups.
6 Sit the cups on a baking tray and transfer the tray to the oven. Bake for 22-25 minutes until the souffles are coming away from the edge of the cups.
7 Remove from the oven and serve with a dusting of icing sugar and a few white chocolate chips on top.