Crush together cardamom, cloves, cinnamon, pepper, cumin and fennel seeds.
To the smallest jar of the mixie add 1/2 tsp turmeric powder, 2 tsp coriander powder, 2 sliced pearl onions, 1 green chilli and crushed whole masala (above ingredients). Grind everything together with 2 tbsp water to a coarse paste.
Heat 1 tbsp oil in a pressure cooker and add remaining sliced pearl onions (10), green chillies (2) and crushed ginger & garlic.
Once it browns, add ground paste and salt. Fry for 3-4 mins, until the raw smell goes and oil starts appearing. Add 1-2 tbsp of hot water, if it sticks to the bottom.
Add cleaned duck pieces and mix well. Once the pieces are coated well with the masala, add coconut milk.
Cover the cooker and cook till, it's done.
Heat 1 tbsp oil in a wide and deep pan. Crackle mustard seeds. Add sliced pearl onion (4-6), curry leaves. Cook till onion browns. Add sliced tomato and cook till it softens.
Add the cooked duck along with gravy. Combine everything well. Cook for another 5-7 mins on lowest flame. Remove from fire. Let the curry rest for at least half an hour for the flavors to develop.