Preheat the oven to 250°F (120°C) and line a baking sheet with parchment paper.
Beat the room-temperature egg whites on medium-high speed until soft, foamy peaks form, about 2–3 minutes.
With the mixer running, add the caster sugar one tablespoon at a time, beating a full 20 seconds between each addition, about 4 minutes total.
Continue beating until the meringue is thick, glossy, and holds a stiff peak. Rub a pinch between your fingers to confirm it's smooth, not gritty.
Sift the cornstarch over the meringue and add the vinegar and vanilla. Fold gently until just combined.
Mound the meringue onto the parchment-lined sheet into an 8-inch circle, creating a shallow well in the center with the back of a spoon.
Bake for 90 minutes without opening the oven door.
Turn off the oven and leave the pavlova inside with the door closed for 1 hour, then crack the door and let it cool fully to room temperature.
Whip the cream to soft peaks and spread it into the well of the cooled shell.
Top with passionfruit pulp, strawberries, and kiwi. Serve within 2 hours of topping.