Heat the water and sugar together to make a syrup. When the syrup reaches 230°F (110°C), start beating the egg whites until stiff peaks form. When the syrup reaches 250°F (121°C), slowly pour it over the egg whites while continuing to beat. Whip until the meringue cools down.

Transfer the meringue to a piping bag fitted with a tip. You can pipe it directly onto a lemon tart or pipe it onto a baking sheet and bake at 210°F (100°C) for about 1 hour and 30 minutes. The meringue will be crisp on the outside and soft on the inside.