Butter and prepare a soufflé tin. Melt 1½ oz. butter, stir in the flour and cook for a few minutes. Add the milk gradually, beating well. Continue cooking until the mixture thickens. Leave it to cool, then beat in the yolks one at a time. Stir in the orange rind, juice and sugar. Stiffly whisk the egg whites and fold these into the mixture. Pour the mixture into the mould; cover with a buttered paper. Steam for 50–60 min. until firm on top.