Peel the mango, remove the seed, and cut it into small pieces.
Take a baking tray and place the mango pieces in a single layer.
Now place the backing tray in a refrigerator for at least four hours or until freeze.
For the moment, put the caster sugar in a heatproof bowl and pour in the boiling water. Stir it with a spoon until the sugar is dissolve.
Add the fresh lemon juice to it and stir again to combine properly.
Cover the mixture with a plastic wrap and place in the refrigerator to freeze.
Take out the baking tray from refrigerator and place the mango pieces in a food processor along with the syrup. Now process it until all the ingredients are mix thoroughly.
Put one tablespoon of the mango mixture in each of the glasses.
Top each of the glass with chilled sparkling wine.
Garnish the glasses with lemon slices and serve.