Preheat your oven to 300°F and line a baking sheet with parchment paper. Draw a 7-inch circle on the parchment as your guide for shaping the meringue base. You'll know you're ready when the oven thermometer hits exactly 300°F.

Pour 3 egg whites into a completely dry, grease-free bowl and beat on high speed using an electric mixer. Start beating for about 1 minute until soft peaks form, then gradually add the 1 cup caster sugar one tablespoon at a time over the next 3-4 minutes. The meringue should go from fluffy clouds to glossy and thick — this took me about 6 minutes total the first time I tried it.

Gently fold in the 1 tsp cornstarch, 1 tsp white vinegar, and 1/2 tsp vanilla powder using a rubber spatula with about 8-10 slow folds. Don't overwork it — you want to keep all those air bubbles intact because that's what creates the signature texture of this strawberry blueberry pavlova cozy.

Spoon the meringue mixture onto your marked circle on the parchment paper, then use the back of a spoon to create a shallow well in the center. The well should be about 1 inch deep and will hold your cream and berries later. I like making the edges a little higher to create a natural border.

Bake for 90 minutes until the meringue is pale golden and feels crispy on the outside when you tap it gently. The center should still have just a hint of give when you press it — don't panic if it looks slightly cracked, that's completely normal. Mine always has a few tiny cracks and tastes just as good.

Turn off the oven and crack the door open about 2 inches — let it cool inside for another 30 minutes. This prevents the dramatic temperature shock that causes big cracks. Transfer to a wire rack and let it cool completely, about 45 minutes to an hour.

Whip together the 1 cup heavy cream with 2 tbsp powdered sugar until soft peaks form, about 2-3 minutes. Gently toss the 2 cups sliced strawberries and 1 cup fresh blueberries with the 1 tsp lemon zest in a small bowl.

Right before serving, spread the whipped cream over the cooled meringue base, then top with your berry mixture. Serve within 30 minutes so the meringue stays crispy on the outside.