To ice pastry, which is the usual method adopted for fruit tarts and sweet dishes of pastry, put the white of an egg on a plate and with the blade of a knife beat it to a stiff froth. When the pastry is nearly baked, brush it over with this and sift over some pounded sugar; put it back into the oven to set the glaze and in a few minutes it will be done. Great care should be taken that the paste does not catch or burn in the oven, which is very liable to do after the icing is laid on.
Or make a MERINGUE by adding a tablespoonful of white sugar to the beaten white of one egg. Spread over the top and slightly brown in the oven.
The Whitehouse Cookbook, by Mrs. F.L. Gillette (Year 1887)