Preheat oven to 320°F. Line two baking tins with parchment paper.In a large mixing bowl, using an electric mixer at high speed, beat the egg whites until soft peaks form. Gradually add the sugar and the cream of tartar and keep beating at high speed. Add the cornstarch and vanilla extract. Beat until stiff peaks form.Pipe the meringue onto the prepared tins. First pipe a small circle and then pipe on top of it, around the edges, in order to form a well.
Put one baking tin in the oven and immediately lower the temperature to 245°F. Bake for 30 minutes, and lower the temperature to about 200°F. Bake until the meringue is dry when touched carefully.Turn off the oven and open the door half way. Leave the meringues inside to cool down. This will prevent the temperature change from being too drastic and causing the meringue to crack.
In a large mixing bowl, beat the mascarpone together with powdered sugar and vanilla until smooth.In another large bowl, whip the cream until thick.Using a rubber spatula gradually add the whipped cream to the mascarpone.
Pipe or spoon the filling into the holes of the mini pavlovas. Top with fresh berries and mint leaves. Serve immediately.
Don’t store filled pavlovas for more than few hours. You can keep pavlova meringues for few days in the fridge, in an airtight container. Place them in the container after they are completely cool. Alternatively, you can freeze them for up to a month. To do that, the best way is to wrap them with plastic wrap as they are on the baking tin with the parchment paper.
Baking properly is the key: To achieve perfectly white pavlovas with no cracks, bake them at low temperature. The best is if you preheat the oven to higher temperature and then gradually decrease it during the baking, until switching the oven off. Don’t take the tin out immediately! You need to leave it to cool down inside the oven, with the door half open. That’s the best way to avoid cracks as they are caused by temperature changes.
Add the topping and the decoration right before serving, otherwise the meringue will get soaked by the moisture, and we want it crispy.
Alternatively, you can just spoon the meringue on the sheets instead of piping, but that way your mini pavlovas will be slightly bigger.