Sterilize glass jars for storing: Place the jars in a pot with water enough to cover them. Bring to a boil over medium-high heat and then just let it gently boil for 10 minutes. Remove the jars from the hot water using tongs and then dip the lids for 10 seconds. Tip the jars and lids over a cooling rack and allow to air dry.
In a non-reactive pan or pot, combine the vinegar, water, sugar, salt, peppercorns, and cloves (if using). Bring to a boil over high heat. Lower the heat and let it simmer for 3 minutes making sure sugar and salt are completely dissolved. Remove from heat and let it cool down.
¾ cup vinegar, ¾ cup water, ¾ cup sugar, 1 teaspoon salt, 10 pieces whole peppercorn, 3 pieces whole cloves
While waiting, prepare the mangoes. Wash and peel the mangoes. Hold the mango stem-side up then cut vertically on both sides along the wide side of the seed to separate the cheeks. Then do the short sides as well to leave just the seed.
2 pounds almost ripe mango
Then cut the cheeks into slices about 1-cm thick. Rinse and drain the mango slices. Arrange the slices inside the sterilized jars, filling them with mangoes as much as you can. If you prefer it spicy, add the chilies to the jar with mangoes.
1 piece hot chili
Pour enough of the pickling liquid to cover the mangoes. Close the jar with the lid.
Let them sit in a cool place for a minimum of 1-2 days. You can also refrigerate too. Longer pickling time will let the flavor seep in better though, however, the mango will stay crisp and crunchy for several weeks only. Unopened pickled mango can last for months or even a year or two if canned properly.
Serve to accompany fried dishes or enjoy as a snack.