Heat a pan and dry roast coriander seeds, cumin seeds, red chillies, peppercorn, cinnamon sticks, and cardamom. Once they start releasing their aroma, add little oil and chopped onions and sauté until the onions turn golden in colour. Add some grated coconut and cook till it gets browned, remove and make a paste of these ingredients in the blender and keep aside. Add some oil in a hot pan; add chopped onions, salt and sauté till the golden turn golden in colour. Add crushed garlic, ginger and green chillies. Add some turmeric powder, garam masala and masala mix (red chilli powder and Malvani masala). To this add 1 cup tomato puree and mix well. Add 1 tbsp of the masala paste (ground at the first). Add crab (cleaned and cut into pieces), water enough to cover all the crab pieces and mix. Cover the pan with a lid and allow cooking for about 10-12 minutes until the crab is cooked. Add freshly ground coconut along with coconut milk to the mixture and mix well. Sprinkle some chopped coriander leaves and switch off the flame.