01 - Preheat oven to 230°F and line a baking sheet with parchment paper.
02 - In a clean bowl, whisk egg whites until soft peaks form. Gradually add caster sugar one tablespoon at a time, beating 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 incorporated.
04 - Spoon or pipe small mounds approximately golf ball-sized onto the prepared baking sheet, spacing them 2 inches apart.
05 - Bake for 1 hour until exterior is crisp and dry. Turn off oven and leave meringues to cool inside with door slightly ajar to prevent cracking.
06 - Combine raspberries, sugar, and lemon juice in a small saucepan. Cook over medium heat for 5 to 7 minutes, stirring occasionally, until raspberries completely break down. Press mixture through a fine mesh sieve to remove seeds. Refrigerate until chilled.
07 - Beat heavy cream, powdered sugar, and vanilla extract together until soft peaks form. Do not overbeat.
08 - Once meringues are completely cool, carefully cut a small hollow in the base of each. Pipe or spoon whipped cream filling into each cavity.
09 - Drizzle filled meringues generously with chilled raspberry coulis. Garnish with fresh raspberries and mint leaves if desired. Serve immediately for optimal texture contrast.