01 - Preheat oven to 230°F and line a baking tray with parchment paper.
02 - In a clean bowl, whisk 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, white 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 to allow for even air circulation.
05 - Bake for 1 hour until exterior is crisp and dry. Turn off oven and leave meringues inside to cool completely with door slightly ajar to prevent cracking.
06 - Combine raspberries, sugar, and lemon juice in a small saucepan. Cook over medium heat for 5-7 minutes, stirring occasionally, 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 and mixture holds its shape.
08 - Once meringues are completely cool, carefully cut a small cavity in the base of each using a sharp knife. Pipe or spoon whipped cream into each cavity.
09 - Drizzle filled meringues generously with chilled raspberry coulis. Garnish with fresh raspberries and mint leaves if desired. Serve immediately to maintain optimal texture contrast between crisp meringue and soft cream.