01 - Preheat oven to 230°F and line a baking tray with parchment paper.
02 - In a clean bowl, beat egg whites 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, leaving adequate space between each.
05 - Bake for 1 hour until exteriors are crisp and dry. Turn off oven and allow meringues to cool completely inside with door slightly ajar.
06 - Combine raspberries, sugar, and lemon juice in a small saucepan. Cook over medium heat for 5 to 7 minutes, stirring frequently, until raspberries completely break down. Press mixture through a fine sieve to remove seeds. Refrigerate until chilled.
07 - Whisk heavy cream, powdered sugar, and vanilla extract together until soft peaks form.
08 - Once meringues are completely cool, carefully carve a small cavity in the base of each. Fill each cavity with whipped cream filling.
09 - Generously drizzle raspberry coulis over filled meringues. Garnish with fresh raspberries and mint leaves if desired. Serve immediately to maintain optimal texture.