Place the sugar in a saucepan with about one-quarter of its weight in water or enough to obtain a wet-sand texture. Make sure there are no sugar crystals along the inside of the pot and that all the sugar has been hydrated.
Begin whipping the egg whites and cream of tartar on medium speed at the same time that the sugar begins cooking.
Cook the sugar to 121°C / 250°F (also known as the soft ball stage).
When the sugar has reached 115°C / 240°F, increase the speed of the mixer to high.
When the sugar reaches 121°C / 250°F, remove the pot from the heat and shock it in an ice bath.
Wait for the egg whites to reach stiff peak and, immediately after, pour the sugar down the side of the bowl and whip until the foam has cooled to room temperature.
Reserve in a piping bag fitted with a #4 plain piping tip in refrigeration. Discard any leftover meringue after service.