- Heat oven to 180C. Grease six individual 180ml-capacity moulds with butter and dust with sugar.
- Melt chocolate in a heatproof bowl over a saucepan of gently simmering water. Stir until smooth.
- Remove to cool a little, then stir in egg yolks (the mixture will thicken slightly).
- Meanwhile, whisk egg whites in a clean bowl until soft peaks form. Whisk in measured sugar a little at a time, and then continue to whisk until mixture is firm and glossy.
- Stir one-third of the egg whites into the chocolate mixture to lighten, then fold through the remaining egg whites.
- Divide mixture between prepared moulds to fill by three-quarters.
- Bake for 20 to 30 minutes until souffles have risen and are just cooked. Serve immediately.