Whisk egg whites to a medium-peak consistency, then gradually incorporate the sugar while maintaining high speed until the mixture is glossy and holds a firm shape.

Fold in the cornstarch and vinegar gently to maintain aeration and stability.

Pipe the mixture into uniform, tall mounds onto a lined sheet pan and bake at 115 °C for 90 minutes. Leave inside the switched-off oven until completely cooled.

Using a small, sharp paring knife, carve a circular aperture into the base of each cooled meringue. Gently loosen the inner marshmallow-like core with a small skewer.

Fill the hollow space with your chosen fruit reduction, then seal the opening with a thick layer of vanilla-whipped cream and invert onto serving plates.