Before you get started, ensure your mixing bowl and whisk are meticulously clean. It's a good practice to wipe them down with a paper towel dampened with vinegar to remove any traces of grease.

Place a cup of water and a pastry brush near the stove. As the sugar cooks, you'll need to brush down any bits of sugar that spatter onto the sides of the saucepan. This helps prevent the sugar from crystallizing.

In a small saucepan, combine the sugar and water and stir just until the sugar is moistened. Clip a candy thermometer to the side of the pan. Heat the sugar mixture over medium heat, without stirring, until it reaches 240°F (soft-ball stage). Use your moistened pastry brush to gently brush down any bits of sugar that spatter onto the sides of the saucepan.

While the sugar syrup is heating, place the egg whites in the clean bowl of a stand-up mixer fitted with a whisk attachment. Add the cream of tartar and whisk at medium-high speed just until the whites are frothy and form a tight network of fine bubbles. Do not whip until billowy just yet; keep the mixer running.

Once the sugar syrup reaches 240°F, immediately pour it into the egg whites in a thin, steady stream near the edge of the bowl (away from the whisk). Increase the speed to high and continue whisking until the meringue is thick, glossy and billowy, and the mixing bowl is no longer warm—about 2–3 minutes.

Transfer to a pastry bag fitted with a star tip. Pipe onto cupcakes and torch if desired.