Add the berries to a pan along with the sugar and water and bring it to a rapid boil. Simmer for 10 minutes, or until berries are mushy and soft.
Remove from the heat and pass through a fine mesh sieve, lined with muslin cloth to remove all seeds and pulp.
Transfer to a sterilised bottle and refrigerate.
Kala Khatta Margarita
For the garnish, Using a peeler, peel the skin from a lemon. Cut a piece into a rectangular shape and then cut the ends into points. slit it in the centre and set aside.
Put a little kala namak on a plate. Wipe the rim of your glass with some lemon juice. Turn the glass upside down onto the salt and twist to coat.
Add some ice cubes into a cocktail shaker and add all the other ingredients and shake to combine.
Add crushed ice into a glasses and pour over the cocktail. Garnish with the lemon and a blackberry and serve immediately.