Preparation

1. Preheat the oven to 350°F with the rack in the middle position. Line a cookie sheet with parchment paper. (If your baking pan is rimmed, invert it so you are using the bottom. This will make transferring the meringue easier once it has baked.)
2. Prepare the meringue. Put the egg whites, cream of tartar, and salt into a large mixing bowl (make sure it is spotlessly clean). Using the whisk, start mixing on Speed 1 and very gradually increase to Speed 3. Whip until the whites form soft peaks. With the mixer running, gradually add the granulated sugar. Increase to Speed 5 and whip until stiff peaks form, about 8 minutes. Add the cornstarch, vinegar, vanilla, and zest, and gently mix on Speed 2 to combine.
3. Transfer the meringue to the parchment-lined baking pan. Shape into an 8-inch circle and, using a spatula or knife, scrape the sides upward, from the bottom of the meringue to the top, to create smooth edges along the sides of the meringue and little peaks at the top.
4. Transfer to the oven and then immediately reduce the temperature to 200°F. Bake for 1½ hours, until the edges and top are dry; the meringue should be very pale. At the end of baking time, turn off the oven, but leave the meringue in the oven until it has cooled completely, about 1 hour.
5. While the meringue is cooling, prepare the topping. Be sure that the oranges have no visible white pith on the segments. Reserve on a plate with the pomegranate seeds.
6. Prepare the orange syrup. Put the sugar and water into a heavy-bottomed saucepan. Cook over medium heat until the sugar has dissolved, then add the juice. Cook until the mixture thickens and coats the bottom of the pan, 20 to 25 minutes. Reserve and cool. NOTE: If the syrup seems too thick to use, you can thin it with hot water, adding a teaspoon at a time.
7. Once the meringue is fully cool, prepare the whipped cream. Put the cream into a large mixing bowl. Using the whisk, start whipping the cream on Speed 1, gradually increasing to Speed 3, for about 1 minute, so that the cream has some body. Add the sugar and vanilla extract, and continue to whip to Speed 4 until cream forms soft peaks.
8. Assemble the pavlova. Put the meringue on a serving plate. Fill with the whipped cream and then, using a slotted spoon, top the whipped cream with the fruit. Drizzle the syrup around the plate. You may garnish with grated zest as well.
9. Serve immediately