Preheat your oven to 300°F (150°C) and line a baking sheet with parchment paper. Draw a 7-inch circle on the parchment as a guide.

In a large mixing bowl, beat the egg whites on medium speed until soft peaks form, about 2-3 minutes.

Gradually add granulated sugar while mixing on high speed for 8-10 minutes until glossy and stiff.

Gently fold in cornstarch, white vinegar, and vanilla extract until just combined.

Spoon the meringue onto the marked circle, creating a nest shape. Bake at 225°F (110°C) for about 60 minutes until dry on the outside.

Turn off the oven and let the pavlova cool inside for an hour with the door ajar.

In a chilled bowl, whip together heavy cream, mascarpone cheese, powdered sugar and vanilla extract until soft peaks form.

Transfer the cooled pavlova to a serving plate, fill with whipped cream, and top with mixed berries.