Step 1: Preheat your oven to 130°C (275°F) and line a large baking sheet with parchment paper. Draw 8-10 circles (about 3-4 inches in diameter) on the parchment, leaving space between them.
Step 2: In a very clean, grease-free bowl, beat the room temperature egg whites with an electric mixer on medium speed until soft peaks form.
Step 3: Gradually add the caster sugar, one tablespoon at a time, continuing to beat on high speed until the mixture is glossy and forms very stiff peaks. The sugar should be completely dissolved. Test by rubbing a small amount between your fingers; it should feel smooth.
Step 4: Gently fold in the cornstarch, white vinegar, and vanilla extract until just combined.
Step 5: Spoon or pipe the meringue onto the prepared circles on the baking sheet. Create a slight well in the center of each pavlova to hold the cream and sauce later.
Step 6: Bake for 1 hour 15 minutes, or until the pavlovas are crisp on the outside and easily lift off the parchment paper. Turn off the oven, leave the door ajar, and let the pavlovas cool completely inside the oven (at least 1-2 hours, or overnight) to prevent cracking.
Step 7: While the pavlovas cool, prepare the blackberry sauce. In a small saucepan, combine 150g blackberries, 2 tbsp sugar, 1 tbsp lemon juice, and 1 tbsp water. Bring to a simmer over medium heat, stirring occasionally, until the blackberries soften and the sauce thickens slightly (about 5-7 minutes). You can mash some of the berries for a smoother sauce or leave them whole for texture. Let cool completely.
Step 8: For the violet cream, combine cold double cream, mascarpone, and 2 tbsp icing sugar in a large bowl. Beat with an electric mixer on medium-high speed until thick and fluffy, but not stiff.
Step 9: Add ½ tsp violet extract and a tiny drop of purple gel food coloring. Mix briefly until just combined and the cream has a pastel lavender hue. Be careful not to overmix.
Step 10: Once the pavlova shells are completely cool, spoon a generous dollop of violet cream into the center of each mini pavlova. Drizzle with the cooled blackberry sauce.
Step 11: Garnish with fresh blackberries and a light dusting of icing sugar before serving immediately.