Preheat the oven to 225°F (107°C). Line a large baking sheet with parchment paper.
Wipe the bowl and whisk attachment of a stand mixer with a fresh lemon wedge or a paper towel moistened with white vinegar. Add the egg whites and beat on low speed until foamy, about 1 minute. Increase the speed to medium-high and continue beating until stiff peaks form, about 3 minutes.
1 fresh lemon wedge , 4 large (120 to 140 g) fresh egg whites
With the mixer running, add granulated sugar, 1 tablespoon at a time, allowing the meringue to return to stiff peaks between additions. Once all the sugar has been incorporated, rub a small amount of meringue between your fingers. If it still feels grainy, continue beating on high speed until the sugar has dissolved and the meringue feels smooth.
1½ cups (300 g) granulated sugar
Meanwhile, melt the semisweet chocolate chips in the microwave in short intervals, stirring between each, until smooth. Set aside to cool slightly while the meringue finishes mixing.
½ cup (85 g) semisweet chocolate chips
Reserve 2 tablespoons of the melted chocolate. Pour the remaining chocolate over the finished meringue and stir once, leaving visible streaks of chocolate throughout.
Dab a small amount of meringue underneath each corner of the parchment paper to secure it to the baking sheet. Spoon the meringue into 6 mounds. The chocolate will become more incorporated as the meringue is portioned, so avoid additional stirring. Use the back of the spoon to make an indentation in the center of each mound for the toppings.
Drizzle the reserved melted chocolate over the pavlovas and use a toothpick to lightly swirl it into the tops.
Bake on the center rack for 1 hour, or until the pavlovas release easily from the parchment. Turn off the oven and leave the pavlovas inside until completely cool.
Meanwhile, add 1 cup (150 g) blackberries and granulated sugar to a small saucepan. Cook over medium heat, stirring occasionally, until the berries release their juices and mostly break down. Remove from the heat and stir in the remaining 1 cup (150 g) fresh blackberries. If the compote is too thick to spoon easily, add a small splash of water. Set aside to cool.
2 cups (300 g) fresh blackberries , 2 tbsps (25 g) granulated sugar
Add the heavy whipping cream and confectioners' sugar to a large mixing bowl. Beat until very soft peaks form.
1½ cups heavy whipping cream, 3 tbsps (23 g) confectioners' sugar
To serve, spoon whipped cream into the center of each pavlova, followed by the blackberry compote. Serve immediately.