Step 1: Preheat your oven to 250°F (120°C). Line a large baking sheet with parchment paper. Draw an 8-9 inch (20-23 cm) circle on the parchment paper (you can trace a plate), then flip the paper over so the pencil mark is on the underside.
Step 2: In a very clean, dry mixing bowl, using an electric mixer, beat the egg whites on medium speed until soft peaks form. This is crucial for a stable Strawberry Sumac Pavlova with Pistachios & Basil.
Step 3: Gradually add the 1 cup of granulated sugar, one tablespoon at a time, beating on high speed after each addition. Continue beating until the meringue is glossy and stiff peaks form. The sugar should be completely dissolved; test by rubbing a tiny bit between your fingers – it should feel smooth, not gritty.
Step 4: Gently fold in the cornstarch, white vinegar, and 1/2 teaspoon vanilla extract until just combined. The cornstarch helps create that famous chewy interior, and the vinegar helps stabilize the meringue.
Step 5: Spoon the meringue onto the prepared parchment paper, using the drawn circle as a guide. Shape it into a mound, creating a slight well in the center and building up the sides slightly. This will cradle your delicious Strawberry Sumac Pavlova with Pistachios & Basil toppings.
Step 6: Bake for 1 hour 30 minutes, or until the meringue is firm to the touch and sounds hollow when tapped. Turn off the oven, prop the door open slightly with a wooden spoon, and let the pavlova cool completely in the oven for at least 1-2 hours (or overnight). This prevents it from cracking and deflating.
Step 7: While the pavlova cools, prepare the strawberries. In a medium bowl, combine the sliced strawberries with 2 tablespoons of granulated sugar and the ground sumac. Toss gently and let them sit at room temperature for at least 20 minutes to macerate, releasing their juices.
Step 8: For the whipped cream, in a chilled bowl, beat the cold heavy whipping cream, powdered sugar, and 1/2 teaspoon vanilla extract on medium-high speed until stiff peaks form.
Step 9: Once the pavlova is completely cool, carefully transfer it to a serving platter. Spread the whipped cream over the well of the meringue, then spoon the sumac-macerated strawberries (with their juices) over the cream.
Step 10: Garnish generously with the chopped pistachios and fresh basil leaves. Serve your gorgeous Strawberry Sumac Pavlova with Pistachios & Basil immediately and enjoy!