Soak red chillies, turmeric powder, black peppercorns, poppy seeds, cloves, green chillies, cardamom pods, cumin seeds, fennel seeds, ginger, garlic, cinnamon in vinegar and 2 tbsp of oil for 30 minutes.
Blend these soaked spices with vinegar and oil also into a fine paste.
Take your lamb pieces into a bowl and add required amount of salt. Apply the blended paste to the lamb pieces and marinate for at least 2 hours or overnight.
I cooked the marinated lamb in a pressure cooker for 5 whistles but you can cook in a pan for 45 minutes or even slow cooker for 2-3 hours.
Heat oil/ghee in a pressure cooker, add the onion slices, sauté them till golden brown in color. Add the marinated lamb in it. Sauté them for a minute. Then add 2.5 cups of water or add water till the lamb is almost covered. Let it go for 5 whistles. Switch off,wait for the pressure to release, open and mix well. If you find it the consistency to be watery, open it and cook for 5-7 minutes. I did open and boiled it for 5-7 minutes over medium heat.
Garnish with coriander leaves and squeeze some lime on it.
Recipe by Relish The Bite at https://www.relishthebite.com/lamb-vindaloo/