Heat the oil in a heavy-based pan over a medium to high heat and fry the chicken, skin side down, until it becomes crispy. It will take about 5 minutes to get a lovely golden colour. You may need to cook the chicken in batches if you have a small pan. Use a slotted spoon to remove the chicken pieces and set aside.
Pour away any excess fat and then, in the same pan, cook the bacon lardons and onions for about 5 minutes until they have taken on some colour.
Add the sweet potato and mushrooms and then return the chicken pieces to the pan, placing them on top, skin side up.
Pour over the stock until it just reaches the chicken skin, add the thyme and cover with a lid.
Leave to simmer very gently for about 10–15 minutes until the chicken is cooked through. The cooking time will depend on the size of the chicken pieces so do check by removing a piece of chicken and cutting into it with a sharp knife.
If you end up having more sauce than you’d like in the pan, simply strain into a clean saucepan, bring to the boil and reduce down and thicken by boiling it.