Beat the egg whites with a mixer on high until they form soft peaks. Add the sugar in to the egg whites by spoonfuls until all is incorporated and stiff peaks form
Blend the cornstarch and vinegar together and whisk into the meringue.
Line a baking sheet with parchment. Using 9-inch cake round, draw a circle on the parchment. Turn the paper over and put it back onto the parchment.
Spread the meringue evenly over the circle, smoothing until even and fairly level.
Put the meringue in the oven and immediately reduce the oven temperature to 300 degrees F. Bake for 1 hour. Turn the oven off and let the Pavlova completely cool in the oven.
For the cherry compote, drain the cherry liquid into a saucepan, reserving 2 tablespoons in a small bowl. Mix the 2 tablespoons of the liquid with the cornstarch and set aside.
Add the sugar to the cherry liquid in the saucepan and heat to a boil, stirring to dissolve the sugar. Add the cherries and the rest of the ingredients and simmer for 5 minutes, or until the mixture has thickened. Allow to cool completely. (Can be made a day ahead of time and refrigerated.)
To make the whipped cream, pour chilled cream into a mixing bowl and whisk on high speed until the cream starts to get fluffy. Add the sugar and spoonfuls of the Mascarpone cheese slowly until all are fully incorporated. Do not over mix. Set the whipped cream aside. (Can be made 4 hours ahead of time and refrigerated.)
To assemble: Place the meringue onto a serving platter and top with the whipped cream. Spoon the cherry compote over the top of the whipped cream. Serve immediately.