Heat the oil in a large, deep ovenproof
casserole and add the onion, cloves,
cardamom, cinnamon and 2 tsp garam
masala. Fry, stirring for 1 min, then add
the paste. Bring to a simmer and season
with salt. Add the chicken, turning each
thigh to coat it, then bring back to a
simmer. Blob the yogurt over the top.