1-Preheat oven: Preheat oven to 350°F (175°C) and line a baking sheet with parchment paper.

2-Whip egg whites: Whip egg whites in a large bowl until foamy. Add cream of tartar and cornstarch; mix well.

3-Add sugar: Gradually add sugar in small amounts while whipping continuously until stiff peaks form (meringue holds a soft hook shape when whisk is lifted).

4-Shape meringue: Spoon six mounds of meringue onto the baking sheet and gently shape into rounds.

5-Bake pavlovas: Place sheet in oven and immediately reduce heat to 250°F (120°C). Bake for 1 hour, or until surfaces are dry and hard and bottoms peel cleanly from parchment.

6-Cool pavlovas: Turn off oven and keep door closed. Allow pavlovas to cool inside for at least 1 hour or overnight.

7-Make the sauce: Combine blackberries, lemon juice, and water in a small pan. Bring to a boil, mashing berries occasionally, until thick and jammy (5-7 minutes). Add a little extra water if too thick.

8-Strain sauce: Strain the blackberry sauce through a fine-mesh sieve to remove seeds; set aside.

9-Whip cream: Whip the whipping cream with powdered sugar and vanilla extract until soft peaks form.

10-Fill pavlovas: Once pavlovas are cooled, carefully crack a hole in the top of each to reveal the cavity. Fill generously with whipped cream.

11-Finish pavlovas: Spoon blackberry sauce over the cream, swirling if desired. Garnish with fresh blackberries.