Drain the soaked beans and place them in a heavy casserole pot with fresh water and turmeric.
Simmer beans over medium heat for 1 to 1.5 hours until tender, adding water if necessary.
Heat oil in a pan and fry onions, garlic, and ginger for 10 minutes until golden.
Add salt, chilli powder, and garam masala, frying for 30 seconds.
Stir in the yogurt and cook the mixture for five minutes.
Add cooked beans and some cooking liquid to the pan and simmer for 10 minutes.
Mash several beans against the side of the pan to thicken the sauce.
Serve the curry with boiled basmati rice and lime wedges.