01 - Preheat oven to 230°F and line a baking tray with parchment paper.
02 - Whisk egg whites in a clean bowl until soft peaks form. Gradually add caster sugar one tablespoon at a time, whisking continuously until stiff, glossy peaks form and sugar is completely dissolved.
03 - Gently fold cornstarch, vinegar, and vanilla extract into the meringue mixture until just combined.
04 - Spoon or pipe small mounds, approximately golf ball-sized, onto the prepared baking tray, spacing them well apart.
05 - Bake for 1 hour until crisp on the outside. Turn off the oven and let meringues cool completely inside with the door slightly ajar.
06 - Combine raspberries, sugar, and lemon juice in a small saucepan. Cook over medium heat for 5 to 7 minutes, stirring occasionally, until raspberries break down completely.
07 - Press the raspberry mixture through a fine sieve to remove seeds. Transfer to a container and refrigerate until chilled.
08 - Whisk heavy cream, powdered sugar, and vanilla extract together until soft peaks form.
09 - Once meringues are completely cool, carefully cut a small cavity in the base of each. Fill each cavity with whipped cream using a spoon or piping bag.
10 - Drizzle generously with chilled raspberry coulis. Garnish with fresh raspberries and mint leaves if desired. Serve immediately for optimal texture.