Butter 4 x 200 ml (7 fl oz) ramekins. Melt the chocolate with the butter in a heatproof bowl set over a saucepan of gently simmering water.
Beat the eggs and sugar together in a bowl until very light and creamy. Sift the flour, then fold into the egg mixture. Fold in the chocolate mixture.
Divide the soufflé mixture between the prepared ramekins. Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 8–12 minutes. The soufflés should rise and form a firm crust, but you want them still to be slightly runny in the centre. Serve immediately dusted with icing sugar, with ice cream or cream.