Whisk together yogurt, pepper powder, turmeric and red chili powder in a bowl. Cut the chicken thighs into small pieces and add to the above mixture. Cover and let it marinate in the fridge overnight.
To make Malvani masala : Dry roast green cardamom seeds, cinnamon stick, cloves, star anise, coriander seeds and cumin seeds in a pan individually till fragrant. Cool the roasted spices and grind in a coffee grinder to a fine powder. This powdered masala can be stored in an air tight container for few months.
Dry roast onion in a small pan. Transfer the onion in a food processor and grind with coconut milk to get a paste.
In a heavy bottom pan heat oil and add cumin seeds. When the seeds splutter add onion and coconut paste. Simmer for about 5 to 7 minutes.
Mix in the tomato puree and cook till oil starts separating.
Add marinated chicken and 1 tbsp of Malvani masala and red chili powder. Let the chicken cook in its juices for few minutes. Now add desired water, bring the curry to boil.
Season with salt and kokum syrup. Cover and cook till the chicken is soft and tender.
Garnish with fresh coriander.