Add the oil to a frying pan and fry the chicken for at least 5 minutes on a medium-high heat, until the chicken is browned
Add the onions, minced garlic, and minced ginger to the frying pan and continue to fry for a further 10 minutes until the onions have softened
Transfer the contents of the frying pan to the slow cooker
Add the remaining ingredients, except for the yoghurt, to the slow cooker
Stir gently to combine. If the curry is looking dry, add a little more stock so that the liquid is just under the level of the top of the curry. If you don't have any more stock, warm water instead is okay.
Cook on high for 3.5 hours, or on low for 7 hours
Stir in the yoghurt, and continue to cook on high for 30 minutes. The curry should now be a nice orangey colour.
Remove the cardamom pods. Sprinkle with garam masala on top for serving (optional).