Heat the oven to 180C/fan 160C/gas 4. Heat 2 tbsp oil in a large casserole with a lid. Season the chicken legs and fry in batches on all sides until golden and crisp, then remove.Add the bacon lardons and fry until some of the fat has been released, then add the onions and celery. Cook until translucent, then add the garlic and fry for another minute before mixing in the flour.Add the cider and let it bubble for a minute before adding the stock, thyme and bay leaf. Bring back to a simmer, season well, and add the chicken legs. Cover with a lid or foil, transfer to the oven for 40 minutes, then remove the chicken and keep warm.