Preheat the oven to 350°F. Generously grease a 15 by 11-inch (jelly roll) sheet pan or rimmed baking sheet, then line it with greased parchment paper.

In a stand mixer fitted with the whisk attachment, combine the egg whites, salt, and cream of tartar (if using) and beat on medium-high speed until medium peaks form, about 3 minutes.

Turn the mixer speed to medium-low and drizzle in the water. Slowly sprinkle in the sugar a little at a time; this may take a minute or so. Turn the speed to high and whip until very stiff, glossy peaks form, about 5 minutes.

Using the whisk attachment or a rubber spatula, gently fold the cornstarch, vanilla, and vinegar into the egg whites.

Evenly spread the pavlova batter in the prepared pan.

Bake until the pavlova starts to turn a light caramel color, about 25 minutes. It will puff considerably while it bakes but will settle once it is out of the oven. Let the pavlova cool completely. (Just leave it in the pan, dust with confectioners’ sugar, and cover with a clean kitchen towel for up to 1 day.)

In a stand mixer fitted with the whisk attachment, combine the cream, confectioners’ sugar, and vanilla and beat on medium speed (you read that right) until just thick—it will start to leave marks from the whisk in the cream.

Remove the bowl from the mixer and, using the whisk attachment, continue whipping by hand for several seconds until the cream reaches the desired consistency; this way, you can ensure the mixer won’t take it too far. Whipped cream is best used right away.

Dust a clean kitchen towel with confectioners’ sugar. Invert the pavlova onto the prepared towel and carefully peel off the parchment paper.

Using the towel to get started, roll the cake, starting at the short end, into as tight a log as you can manage. Transfer the log to a serving platter. Cover with plastic wrap and refrigerate for 1 hour.