Italian meringue requires heating a sugar syrup to a precise temperature of 118-121°C before pouring it into whisking egg whites. This cooked sugar syrup effectively pasteurises the egg whites, creating a stable, glossy meringue that holds its shape without baking. A sugar thermometer is essential — going too low means the meringue won't set properly, and going too high risks caramelising the sugar or scrambling the eggs. Always add a splash of water to the sugar in the pan before heating; without it, the sugar will caramelise rather than form a syrup. Pour the hot syrup in a slow, steady stream into the egg whites while the mixer runs.