Preheat the oven to 350 degrees F, and line a baking sheet with parchment paper.
In a stand mixer fitted with the whisk attachment, whip the egg whites, cream of tartar, and salt on medium high speed for 60 seconds, until foamy.
Add the sugar, cornstarch, vinegar, and vanilla and continue whipping on high speed for 2-3 minutes, to stiff peaks.
Dollop the meringue onto the parchment paper in 6 individual mounds. Carefully shape them with a spoon, making sure they’re not more than 1.5 inches tall.
Bake in the middle of the oven for 10 minutes, then turn the heat down to 300 degrees. Continue baking for another 40 minutes. Over this time, your meringue will puff up, take on a lightly browned color, and crack slightly. Turn the oven off, and prop your oven door open slightly so your pavlova can cool very gradually. Leave it in the oven with the door propped for at least 30 minutes.
To Make the Chantilly Cream:
Pour the heavy cream into a bowl, and whip with a hand or stand mixer for about 30 seconds until it thickens slightly. Add the sugar and vanilla extract, and continue mixing until you get soft peaks.
To Make the Blackberry Compote:
Combine all ingredients in a saucepan, and cook on medium heat for 8-10 minutes, until the blackberries soften and release their liquid.
To Assemble Each Pavlova:
Place a meringue on an individual serving plate, then add a few spoonfuls of Chantilly cream, followed by a few spoonfuls of blackberry compote. Serve promptly, and enjoy!
Recipe adapted from Ina Garten.As with any meringue, make sure your bowl and whipping utensils are spotlessly clean, and take care not to get a single drop of egg yolk mixed with the egg whites. Any small speck of dirt, drop of oil, or fat (from the egg yolks) may prevent the egg whites from whipping up.