Pressure cook tamarind with little water for 2-3 whistles in medium flame.
Extract juice with 1 cup water.
Optional step: Heat jaggery with 1/4 cup water, strain it to remove impurities.
Heat jaggery + tamarind extract in a sauce pan.
Mix kala namak (black salt), chaat masala, roasted cumin powder and red chilli powder using a whisk.
Bring to boil. It may overflow first, so keep mixing.
Simmer for 6-8 mins until it becomes thick, glossy and sticky.Cool down to store.