To make the meringue: Preheat the oven to 350°F with a rack in the center. Line a baking sheet with parchment. In the bowl of a stand mixer fitted with the whisk attachment, whisk the granulated sugar, cream of tartar, and salt until evenly combined. Add the egg whites and beat on low speed (speed 2 or 3 on a KitchenAid) until the mixture looks creamy and the sugar granules have dissolved, 8 to 10 minutes. (Rub some of the egg white mixture between your fingers to make sure you feel no graininess.) Increase the mixer speed to medium-high (speed 7 or 8 on a KitchenAid) and beat until stiff, glossy peaks form, 6 to 8 minutes. Sift in the confectioners’ sugar, add the vanilla, and beat, starting on low speed and increasing to medium-high, for 20 to 30 seconds, stopping to scrape the bowl as necessary. At this point, all of the confectioners’ sugar should be incorporated into a stiff, glossy, voluminous mixture. Mound the meringue on the baking sheet. Using a rubber spatula or the back of a large spoon, spread the meringue into a 7" to 8" round or oval, working from the center outward while slightly hollowing out the center. Aim to have a concave center surrounded by a 1" border that’s about 2" tall. Reduce the oven temperature to 225°F and bake the meringue, without opening the oven door, for 1 hour. With the door still closed, turn off the oven, and leave the meringue inside, undisturbed, for at least 2 hours and preferably overnight.

To assemble the pavlova: About 1 hour before serving, set aside about one-quarter of the peppermint bark. Melt the remaining bark in the microwave in 30-second increments, stirring between each, until smooth. Pour it into the center of the meringue and use the back of a large spoon to spread it evenly over the bottom and up the sides. Set the meringue aside until the chocolate is set, 30 to 60 minutes, depending on your room temperature. (If your room is particularly warm, transfer the meringue to the freezer for 5 minutes, or while you whip the cream, to set the chocolate.) In the bowl of a stand mixer fitted with a clean whisk attachment, beat the cream, confectioners’ sugar, cocoa powder, vanilla, and peppermint oil to soft peaks. Taste and adjust the peppermint flavor as desired. Spoon the whipped cream into the center of the pavlova, covering the chocolate. Top with the reserved peppermint bark. Serve immediately.