In a heat-proof mixing bowl (preferably the metal bowl of a stand mixer), add the egg whites, granulated sugar, cream of tartar, and a pinch of salt.

In a separate saucepan (small enough that the metal bowl can rest over the water, but not fall in), bring a couple inches of water to a low boil.

Carefully set the mixing bowl with egg whites and sugar over the boiling water (similar to a double boiler). Whisk the egg whites until the sugar is completely dissolved (about 2 minutes). Rub a bit of the mixture between the pads of your fingers, you should not feel any sugar granules.

Add the vanilla to the egg white mixture.

Place the mixing bowl on the stand mixer. With the whisk attachment, beat the egg white mixture, starting on low speed and working up to high speed, until stiff peaks form (about 3-5 minutes).

Transfer the whipped meringue to a piping bag fitted with tip #1M.

Preheat the oven to 200°F. Line two baking sheets with parchment paper.

Pipe swirls onto the parchment paper, about 1 inch apart.

Bake for 1½ hours, then turn off the oven, leaving the door closed and the cookies inside for an additional 1 hour.

Meringue cookies are very susceptible to moisture/humidity in the air. After removing them from the oven, allow to cool (this should only take 10-15 minutes) and then immediately transfer to an airtight container (I like to use a Ziploc baggy.) Store in a sealed airtight container on the countertop for up to one week.