Using a whisk or electric mixer, whip the egg whites and salt into peaks. Add the vanilla, and continue beating to stiff peaks.
Stir the cream of tartar into the regular sugar and whisk into the whites very gradually, a spoonful at a time, until the meringue is stiff and the sugar has dissolved.
Sift together the icing sugar and cornstarch. Sift over the meringue and gently fold until fully incorporated.
Pipe or spoon the meringues onto a parchment-lined baking sheet. Bake at 225 degrees F/110 degrees C until cream-coloured and crisp on top when tapped, 1 to 1 1/2 hours.
Remove the meringues from the oven. Cool on the trays. Store in an air-tight container.