Preheat the oven to 250°F / 120°C. Line a baking sheet with parchment paper.

In a stand mixer fitted with the whisk attachment, beat the egg whites on medium speed until foamy, about 30 seconds. Turn down the speed to medium-­ low and slowly drizzle in the superfine sugar. Once all the sugar is added, turn the speed to high and whip until it is light, fluffy, glossy, and there is no graininess left in the meringue, about 5 minutes. Add the vinegar and vanilla and continue beating at high speed for 30 seconds.

Spoon the meringue onto the prepared baking sheet in six equal-­size blobs (you can make them smaller or larger, but it will affect the baking time), spaced about 3 inches apart so they have room to expand. If you are flavoring the meringues, sprinkle or drizzle your preferred topping over the meringue and swirl it in using the tip of a knife or a chopstick. Don’t overwork it or the meringues may spread too much.

Bake for 1 hour, then reduce the heat to 200°F / 95°C and continue baking for 30 more minutes. Turn off the heat and leave to sit in the oven for about an hour to make sure the outside stays crisp, but the inside has a bit of chew. It may require longer depending on the oven and if you want a crispy interior.

The meringues can be stored in an airtight container for 24 hours.