Whisk the egg whites until stiff peaks form. Gradually whisk in the sugar, then whisk for a few minutes more until the mixture is thick and glossy (see
Mix the cornflour and vinegar together until smooth. Fold into the meringue mixture.
Spoon into a 33 x 23 cm (13 x 9 inch) Swiss roll tin lined with nonstick baking paper snipped diagonally into the corners and standing a little above the top of the sides. Spread level. Bake in a preheated oven, 190°C (375°F), Gas Mark 5, for 10 minutes until biscuit-coloured and well risen. Reduce the heat to 160°C (325°F), Gas Mark 3, for 5 minutes until just firm to the touch and the top is slightly cracked.
Cover a clean tea towel with nonstick baking paper and sprinkle with a little sugar. Turn the hot meringue out on to the paper, remove the tin and leave to cool for 1–2 hours. Meanwhile, simmer the apricots in the water for 10 minutes until tender. Cool, then purée until smooth.
Peel the lining paper off the meringue when ready to serve, then spread with the apricot purée. Whip the cream until it forms soft swirls, then fold in the fromage frais and spoon over the apricot purée.
Roll up the meringue to make a log shape, starting from a short side and using the paper to help. Transfer to a serving plate and cut into thick slices to serve.