Line a 26 x 30 cm (10 x 12 in) Swiss roll pan with greaseproof paper painted with oil.
Beat egg whites with salt until stiff peaks. Beat in three-quarters of the sugar, 2 tablespoons at a time. Gently fold in remaining sugar, cornflour, vinegar and vanilla and spoon into prepared pan.
Smooth over with a pastry spatula.
Bake at 175C (350F) for 12-15 minuces or until it is set on the top and resilient to the touch. Turn out onto a cake cooler covered with a clean tea-towel sprinkled generously with caster sugar. Leave 5 minutes.
Roll up gently from a short end, using the tea-towel to assist you. Leave for 30 minutes or until cool.