Preheat oven to 120°C. Line a baking tray with parchment paper.
In a large bowl, beat the egg whites with a pinch of salt and cream of tartar until they start forming soft peaks. Gradually add the caster sugar one tablespoon at a time. Turn the mixer to high speed and beat the mixture for a few minutes, until it is shiny and stiff peaks start to form. Get a bit of the mixture and rub it between your fingers to see if your meringue is ready. If you can still feel sugar granules, then beat it a little longer until the grains are all dissolved.
Spoon your mixture onto your prepared baking tray, into not so perfect circles (about 10 cm in diameter and 2-3 heaped tablespoons of meringue per pavlova) Use a spoon to make an indentation in the middle of each meringue.
Bake the meringue for 15 minutes at 120°C, then reduce the temperature to 100°C and bake for another 45 minutes.
After 45 minutes turn off the oven, open the door and let your meringues cool in the oven for another hour. The meringues are ready when they come away from the parchment paper without sticking at the bottom.
Puree the thawed raspberries in a blender. Strain the mixture through a fine mesh sieve and mix in the icing sugar. Refrigerate until ready to use.
Whip your heavy cream with the vanilla sugar, until stiff peaks form. Keep your cream refrigerated until you are ready to assemble.
To assemble your pavlovas, place a meringue on a plate, layer with a dollop of whipped cream, followed by a tablespoon of raspberry sauce and top it off with fresh berries and a mint leaf.
Serve your pavlovas immediately. The meringue will get soggy if you assemble them in advance. The meringue shells, however, can be made in advance and stored in an airtight container. The raspberry sauce and whipped cream can also be prepared in advance and stored in the fridge.