Preheat your oven to 250°F and line a baking sheet with parchment paper. Grab a mixing bowl and make sure it's completely grease-free—even a tiny bit of oil will sabotage your meringue. I learned this the hard way when I used a bowl I thought was clean, and the whole thing flopped.

Add 4 egg whites to the bowl and beat with an electric mixer on medium speed for about 1 minute until foamy. Sprinkle in the cream of tartar, then keep beating until soft peaks form (the peaks flop back on themselves). This takes roughly 3-4 minutes total, and you'll see it transform right before your eyes.

Gradually add 1 cup granulated sugar, one tablespoon at a time, beating continuously on medium-high speed. Keep going until stiff, glossy peaks form—you want the mixture to look like shiny, thick clouds. This step takes about 5-6 minutes, and honestly it's weirdly satisfying to watch.

Gently fold in the cornstarch, cream of tartar (if adding separately), and vanilla essence using a spatula. Don't overmix here—you'll deflate all those beautiful air bubbles you just created. Fold just until no streaks remain, maybe 15-20 gentle folds.

Spoon the meringue onto your parchment-lined baking sheet, creating a flat circle about 10 inches wide. Use the back of a spoon to create slight ridges and peaks across the top for visual interest. Bake at 250°F for 1 hour and 30 minutes until the outside turns pale golden and feels crispy to the touch.

Turn off the oven and crack the door open about 2 inches, then let the strawberry blueberry pavlova party meringue cool completely inside for at least 1 more hour. This gradual cooling prevents cracking, which I discovered after my oven-shocked first batch cracked into three pieces. Patience here saves the entire dessert.

While the meringue cools, whip 1 cup cold whipping cream with 2 tbsp powdered sugar until stiff peaks form. Toss 1 cup sliced strawberries and 1 cup blueberries with 1 tsp lemon juice in a separate bowl, letting them sit so the juice releases slightly.

Once the meringue is completely cool, transfer it carefully to your serving plate. Spread or dollop the whipped cream over the top, then arrange the berries in any pattern you like. Sprinkle 2 tbsp chopped pistachios over everything for crunch and color, then serve immediately.