Pre-heat oven to 140°C and line a baking tray with baking paper.
Place the egg whites and sugar in a heatproof bowl set over a saucepan of gently simmering water (do not let the bowl touch the water). With electric beaters, beat constantly for 6-8 minutes until the sugar has dissolved and the mixture is thick. Remove from heat, continue to beat for 10 minutes or until the meringue mixture is cool, stiff and glossy. Fold in the corn flour and vinegar.
Place dollops of meringue mixture on the baking tray; make a shallow indent in the top of each with the back of a spoon. Bake for 1 hour, then turn off the oven and allow the meringues to cool completely in the oven with the door slightly ajar.
Meanwhile, for Mango Mint Sauce: combine mangoes, lime juice and Fountain Mint Sauce in a small food processor or blender, process until smooth.
Serve meringues with Mango Mint sauce, garnish with mint leaves.